Mileage and trailer towing mods?

[Dennis S]

I'm hoping that someone can give some advise on what to do next. I'm trying to get better gas mileage, currently it's averaging about 14mpg city driving ~ 20 miles each day. I'm also trying to get my truck set up to pull a camper, (approx 16' travel trailer or tent trailer). I know the max towing capacity for this truck is listed as 5200 lbs. I intend to be below that depending on which trailer I can borrow/rent but the travel trailer/truck could be pushing 4500 lbs easily when loaded.

The few mods I've done have made a slight difference in mileage and in the eat-of-my-pants-dyno. I wish it had more low end torque. The engine seems to grunt and rpms are slow to climb until about 2500 and then pulls pretty hard and rpms climb fast.

The first likely place I would venture out with this rig is a fairly steep climb/descent. I'll only be going about 40-45 miles but a 15 mile stretch climbs ~ 5000 ft.

Other information:
- 62,500 miles, I'm the third owner.
- This truck has the 4.3L, 3:42 gears, stock tires and rims.
- The front of the airbox has been cut off and K&N filter installed
- Modified throttle plate (about half of deflector removed with Dremel)
- 160° thermostat installed
- Trailer brake controller, a Tekonsha PRIMUS, currently in progress of being installed

Things considered...
a) I've thought about a cat-back exhaust, both Magnaflow or Flowmaster are carried at the local exhaust/muffler shop.
b) I've considered Hypertech Programmer but not convinced it's worth the investment.
c) Will the engine/transmission handle this with a 3500-4000lb trailer in tow?
d) Thought about Airlift bags to prevent rear-end squat... I need to check the truck with a realistic load in the back to simulate a trailer and loaded with equipment/supplies/passengers. I already know that a load of gravel will push it down to the bumpers.
e) I know that 3:73 or 4:10 gears would be better for towing and possibly for mileage but can't afford to replace both ends so I'm leaving it alone.
f) Would synthetic or semi-synthetic oil throughout drive-train be a significant benefit?

Am I progressing on the right path? Can anyone answer the questions/ concerns I have? Any thoughts on which way to go next?

Thanks in advance for any input,

[T Man]

Other information:
- 62,500 miles, I'm the third owner.
- This truck has the 4.3L, 3:42 gears, stock tires and rims.
- The front of the airbox has been cut off and K&N filter installed
- Modified throttle plate (about half of deflector removed with Dremel)
- 160° thermostat installed
- Trailer brake controller, a Tekonsha PRIMUS, currently in progress of being installed

Things considered...
a) I've thought about a cat-back exhaust, both Magnaflow or Flowmaster are carried at the local exhaust/muffler shop.
b) I've considered Hypertech Programmer but not convinced it's worth the investment.
c) Will the engine/transmission handle this with a 3500-4000lb trailer in tow?
d) Thought about Airlift bags to prevent rear-end squat... I need to check the truck with a realistic load in the back to simulate a trailer and loaded with equipment/supplies/passengers. I already know that a load of gravel will push it down to the bumpers.
e) I know that 3:73 or 4:10 gears would be better for towing and possibly for mileage but can't afford to replace both ends so I'm leaving it alone.
f) Would synthetic or semi-synthetic oil throughout drive-train be a significant benefit?

Am I progressing on the right path? Can anyone answer the questions/ concerns I have? Any thoughts on which way to go next?

Thanks in advance for any input,


One gigantic piece of info at a time.

Freeing up exhaust and intake will give you the biggest benefits without going internal. Have the local exhaust shops do the catback system. If you want to see more good gains, a set of headders and y pipe. I think the sites store carries them, but im not sure which brands. A cold air type intake will also give you mild to moderate benefits. You can go as mild or wild on it as you want and go supercharged and whatnot, but thats up to you. I would suggest 3.08 gears for highway mileage (lower number, better mileage, higher number, better preformance, but higher highway rpm), but since you are pulling a trailer on a regular basis, stick with the 3.42 gears to give you better off the line grunt. As far as synthetic v. non synthetic, you will hear as many different stories as there are types of oil. I ran synthetic and have noticed a improvment in mileage by about 40miles a tank. This could verywell be different for you. As far as the trans. Id invest in a transmission cooler. Coooler temps=longer life, and our 700r4's tend to get a little warm. Replacing the fluid and filter wouldnt be too bad of an idea either.

Hope this could be of help to you.

[Dennis S]

Sorry about that, I didn't realize how long it would get. I've been doing a few mods on the cheap. I know that the next few steps will start getting expensive. I thought that getting the rpms up closer to the power band might help with city driving mpg. I had thought about a transmission cooler but then it looked to me like the lines already run to the radiator. Would an auxiliary cooler make a lot of difference for the 4L60E temps? I've read/heard a lot about synthetics in the engine, diffs and possibly transfer case... any thoughts about the transmission? Any difference between straight synthetic and a blend? I know... lots of different opinions.

[20Xtreme02]

I'd certainly second changing the muffler to a less restrictive one, it improved my mileage by almost one and a half miles per gallon. I don't think replacing the pipe aft of the muffler via a cat-back system will do anything for the mileage. I have also used a programmer (in my case a Superchips) but I haven't seen any increase in mileage from it. There was a definite increase in power which would be advantageous for pulling.

[Sparky2263]

You'll be pulling in 3rd gear so the 3.42's are about perfect. 3.73's would be ideal but the difference can be made up in the exhaust. It'll be grunting so you want to free up the exhaust as much as possible.

A 15,000 GVW tranny cooler is a MUST. You will burn up that 4L60E pulling that kind of load without it. Incoming fluid to the cooler THEN the radiator. No sense making the radiator cooler work harder than it needs to.

I would invest in a load leveling hitch since you will be near peak capacity. It'll make all the difference when trying to tow at interstate speeds. Without it you'd peak at around 60 before having sway problems. With it you can run 80 all day long. BIG difference in safety.

Synthetics would be considered a must in the diff, helpful in the trans (very) and optional in the engine.

For mileage, ditch the 160 t-stat and put in a 180 or 195. The 5hp or so loss will not be missed as the mileage increase would prolly be at least 1mpg. Much better for towing anyway.