what tranny should I go with?

[BLUE THUNDER]

Well guys, I'm sure that this has been discussed at least a couple of times already but...... I'm in the middle of pulling out my Th350. After i got the new motor in and running the tranny decided to dump all its fluids on my garage floor. (BTW, I also posted this question on the drivetrain section with 0 answers so far). I figure my blazer and jimmy bro's wld have answers for me. I'm planning on some light wheeling, road trips, and possibly towing an R.V. Since I've never driven my Blazer I don't know what the rpm's are at highway speeds. I've heard at about 70mph they are pretty high. If anyone knows exactly what rpm it is please let me know. My questions are 1) is the Th350 strong enough for what i have planned? I shld mention that it has a 4" lift and 33's with 3.73 gears. My second question is what is the benefit of going with a Th400 or 700r4. How difficult are these swaps if i wanted to retain the np205? I really need some feedback to make a good decision. Thanks, Mario