34MPG in a GIANT truck

[comptiger5000]

Newer vehicles definitely make more aggressive use of TC lockup, which helps FE. When I eventually do some computer tuning on my Jeep, one of the planned mods is more aggressive use of TC lockup.

[ECONORAM]

Originally Posted by bandit86

why dont you guys buy taller tires? go form a 25 inch tire to a 27 inch tire, should fit, instant 8% gear reduction. I know they're heavier but might work better. my old chevy tracker loved 70-80km on sideroads with 33s. those were 25% bigger then stock, I barely touched the gaspedal. Also had a snorkle

Running taller tires can help. Dodge does that with any truck that comes out with factory 20" wheels. The rear gears are 3.92, but the 33" tall tires change that to 3.55 gears. It does make accelerating harder though.

Originally Posted by comptiger5000

I wish my Jeep was geared that tall. I turn 2k RPM at 67 mph, so about 1500 at 50. It could do less, as it'll pull well at 1100 - 1200 in OD with the TC locked.

My RAM turns about 2k at 70mph, but I noticed it would drop a couple rpms if I bumped up the transmission fluid pressure. Do you have a 545RFE trans? Try a Transgo shift kit, or at least the resistor mod.

I have installed some aero panels on my truck and tested it today with the massive (25mph) head/tail winds we had in OKC today, and my two way average was 23.7 mpg. Not too bad for a 5250 pound truck. 65mph ave speed, no a/c. 80*, running 89 octane fuel.

[comptiger5000]

I don't have the 545RFE. I have the older (and less fuel efficient) 46RE. Next time I drop the pan, I'm debating between a shift kit, and simply cranking the line pressure screw a few turns. Fortunately, I don't mind the firm shifts.

FWIW, mine has 3.73 axle gears, the tranny ratios are: 2.45, 1.45, 1, 0.69. Tires are 225/70/16 (will be replaced with 245/70/16 when these wear out to use all available tire clearance)

[ShadeTreeMech]

comptiger, sounds like you have similar gear and final drive ratios as what i have in my Maxima. What will adjusting the line pressure crew do, besides somewhat firmer shifts?

I had an Isuzu pickup with such frim shifts that if it shifted from first to second when I was cornering it would bark the inside wheel everytime. Bad thing was it may have contributed to the early demise of my U joint.

[comptiger5000]

It will firm up the shifts a bit, as well as increase the holding power of the clutches. This minimizes slippage, giving a longer transmission life (less clutch wear), and possibly a slight mpg increase (if it slips a little under load).