Re: Gearing......I've never been much of a fan of the .86 T5 because of the very short 1st gear. Having run the .72 T5 with the 3.76 low gear, 28" tall rear tire, I've found in over 13K miles that you are shifting out of low gear half-way through an intersection. However, crunching your numbers and looking at the upper gears I think your truck might be really happy with the 30", .86 OD, 3.90 combo if most of your driving is in 60 mph range.
FYI:
http://csgnetwork.com/multirpmcalc.htmlIn setting up my gearing I calculated that I would be doing most of my cruising at 70 mph and geared my 54 truck to run at 2000 rpms. Problem is that at 70 mph@2000 rpms I'm just getting into the sweet area of the torque curve. Increasing my ground speed to 75-80 mph ( 2216-2364 rpms) brings my vacuum up appreciably but puts me in danger of catching a fat speeding ticket.
My problem was over-estimating my "normal" cruising speed. In reality most of my cruising buddies like to putz along at 60 mph which has me even lower in the torque curve and not letting my engine breath efficiently. Crunching your numbers you'd be turning 1878@50 mph, 2254@60 and 2630@70 mph.....which would let you drop down to 40 mph in 5th gear without a downshift and would let you run at a legal 70 mph@2630 which wouldn't be excessive for a healthy 235. Granted the 4.03 would have you short shifting out of low very quickly but the 3.76 1st gear transmission wouldn't be that much of an improvement.
I think that Crenwelge's advice to go with the .86 box would work out for you in the long run. Hope this helps.
Dave
