I have a 1987 toyota I have converted a 4.3 litre vortec into. And my transmission is starting to slip,the transmission I have now is a 700R4,I have
been told by a few people I should put a turbo 350 in it instead of another 700R4.I would have to change my transfer case adapter,and I dont know if Iwould have any wireing issues with my vehicle control module.So I am wondering if it would be worth swapping to a turbo 350,or if I should just get a heavy duty 700R4?

Stick with the 700R4 - the transmission is based on the 350 and can be just as strong when built properly, plus you get to keep the overdrive. Fuel is expensive these days.