I have 02 Dodge Ram with a 4.7 and 45rfe Trans with 3.92 rear. I can change the TCM to a Jeep unit and gain an extra overdrive gear. The trans has a 3:1 1st gear and a .75 overdrive in 4th.The TCM will add a .67 5th gear. Is my math correct in that 3x3.92=11.76 overall first gear and if I go with a 4.56 rear 13.68. With 32" tires I would increase cruise rpm by about a 100 rpm. This sounds like a no brainer to me. With the whopping 295 lbft of torque advertised I would go from 3500 to 4000 lbft in 1st. Others have done this without changing rear gears and the results were mixed with the size of the truck, load,terrain etc. I really don't see a downside if I do both. I have all the tools and have done many 9.25 rears so I'm looking at a TCM at about $50, a set of gears, narrowed cross pin and bearings. About 4-500 bucks.
What are your thoughts and am I missing something. 500 foot pounds more in first with a 100rpm increase at 75 or so for 500 bucks sounds like a bargain to me.
Transmission to Rear-end
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