If your rig requires a lot of almost full throttle in O/D, then going to a 4:56 or 4:88 would you to use less throttle to maintain the same speed because the engine is in its power band and operating more effecently. Most O/Ds are like 15-20% the Toyota O/D is 29% way to much for a MH. Its almost to much for an empty pickup on anything but flat ground, but it made for good EPA numbers
If you turning 3700 in 3 with out O/D and thats how you normally drive it. Then going to a 4:88 would let you use O/D more often with out lugging the engine. A 4:88 would let you turn around 3400 in O/D making the engine run with a higher manifold vacuume, getting better gas milage and better acceleration. So you can have your cake and eat it too if you make some correct chioces.
Big slow turning V-8's are a whole different animal.
WME