someotherguy
+1y
Well here's the catch. You said you don't want an electronic transmission, so that limits you to the only non-electronic automatic strong enough to put behind a big block or in any truck heavier than a 1/2 ton, the TH400. So right off the bat you lose overdrive, your gas mileage goes downhill, and your engine RPM's at highway speed will be several hundred higher. You'd also have drama hooking the speedometer up because the majority of TH400's are cable-drive speedo; it's only a very rare few that were electronic speedo, the first few years of OBS some trucks had them. For example I was just posting in another thread an 89 1 ton OBS I'd bought, that's TH400, they didn't start with the 4L80E until 91. As for the passing gear there's no linkage for it, it's electronic on the TH400, you can rig a switch on your throttle linkage or under the pedal that gets triggered at WOT.
Now back to what would actually work best, the 4L80E, and you'd need to get one from a 96 or newer to work in your truck. Get the trans, engine compartment wiring harness, and PCM or have yours reflashed for an automatic. You'll also need the steering column, shifter cable, and a radiator with the cooler built in - an external cooler alone won't cut it esp on a big truck. Best setup is radiator cooler + external cooler, the way the factory did it.
You will probably also need to remove the pilot bushing in your crankshaft so the "button" on the front of the torque converter doesn't bottom out on it and not seat properly. Some people just drive them further in but to me that's a hack and if you ever want to use a standard with that engine later you may have to have the thing machined out and a new bushing put in. Lisle makes a sweet tool for removing the bushing and it's not expensive.
Richard