I'd build a 700r4 up. Lower first and 2nd gear, ie 3.1 vs 2.48. It has an OD as the 4l80 has. That was my choice back when I had an 88 ext cab, after going thru 2 or 3 th400' in 100K miles of towing. 2nd gear would not hold in a manual position. Never rebuilt it again, finally sold it. Another rig, an 89 R3500, used to go thru TH 400's like clockwork every 40K miles, even with 7-8K mile tranny fluid changes. The later 4l80e trannys seem to be better and longer lasting than the TH400 in my experience. The 700r4 as mentioned before re the th400, it is all manual and you do not need the stand alone computer.
05 Chev CC D/A LS Dooley
92 Navistar dump truck, 7.3L 7 sp, 4.33 gears with a Detroit no spin
00 Chev C2500, V5700, 4L80E, 4.10, base truck, no options!
92 Red-e-haul 12K equipment trailer
3 Single axle utility trailers
I to would go with a built 700r4. I put a Bowtie Overdrives stage 3 in my 91 Suburban. with manual torque converter lockup. Worked great. The lockup will keep the heat down when towing. Had a 4l80 in mt 93 K2500 never had an issue with it and it still in use. But I found no way to lock up the TC. So it would unlock at every rise in the roads at highway speed towing. This made it hard to keep cool. Computers to run 4l80 are pricey.
1997 Ford F250 Extended Cab, 7.3 Diesel, 8 foot bed.
Reese 16K Hitch
(Moved into Shed) Hensley Arrow
Jordan Brake Controller, Hensley TruControl Gold Shelved.
Open Range 5th Wheel, Roamer RF392 BHS
-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...
I had a 83 GMC Suburban C 2500 w/454 Turbo 400 3.75 ratio (80K miles when we sold it) towing our 89 Avion 7600# and never had any problems. We bought a 2001 Chevy Suburban C 2500 8.1L w/ 4L80 trans. 4:10 ratio and have 48K mileage towing the same trailer and no problems. The original owner towed a horse trailer for a year before we purchased it from and had no problems. The OD with the 4L80 is so much better, more power and better economy when in OD.
I would choose the 4L80 over the Turbo 400 which is a 3 speed vs. a 4 speed.