I have an 89 model 700r4 in my 85 3/4 ton suburban with a small block 400 and 3.73 rear. I tow a 8600 pound boat with it and never have a problem, I even tow in OD which everyone says not too, but the 400 just hums along without so much as a hickup. It has been built with some aftermarket goodies, but nothing expensive. I think part of using the 700r4 is having enough torque and rear gear that you don't keep locking and unlocking at lower rpms without having so much torque that you munch the thing.
