Transmission Recommendation

[86-C10-V6]

My truck currently has a rebuilt 700R4 transmission. It was rebuilt in 1992 with 108K miles and I have used the truck mainly for hunting(pretty rough on the tranny) and hauling trash to the dump, it has 160K on it now and the transmission is whining and recently it refused to shift to high gear. The transmission mechanic that rebuilt the tranny said it probably had metal shavings in the pan and would cost about $1200 to rebuild including remove and install.
I am thinking of changing to a 350 or 400 transmission that does not require a TCC lock up.
The V6 seems have difficulty keeping the TCC locked in high gear and the added RPMs without the overdrive I think would help the response.
1)Which transmission would handle more abuse the 350 or the 400?
2)Which would be easier to install in the place of the 700R4?
3) What would be required for each of these swaps?
4) Should I just go buy a cheap rebuilt 700R4($550) and install myself and run it in 3rd gear.