how good is overall engine performance 5.7 V8

Poorly, they have 180 horsepower out of a stock 350. I have had 3, 1 2wd and 2 4wd. My truck with 120000 miles pinged towing my 18 foot boat. My latest truck has 90000 original miles. It runs better, but unless you have 3.73 gears and a moderately built engine I wouldn't even try it.

I wouldn't plan on doing it regularly if you have anything higher than 3.73 gears. If you have the 700r4 trans keep it out of overdrive to reduce the load on the engine and increase your rpm's and torque. i have pulled 6-7000 with 3.73's and a 305 on my 84 with a little pinging but I was running the overdrive (which I now know not to do). Don't expect much but it should do fine if you're in mechanically good condition. I have an 86 sub with a 350 3.42 gears myself and would not hesitate to put up to 6000 behind it on a short under 100 mile trip on fairly flat ground. If i had 3.73 or lower I'd go heavier.

Everything else runs fine, I just continue to have maintenance problems with it's transmission; I've replaced it twice with two different re-built transmissions and that was after spending two or three hundred dollars or so trying to repair the original one. It started off with just a simple leak in the transmission, it was downhill from there. Any suggestions? Or should I just junk it?

Add an extra transmission cooler get one with an electric fan if you can afford it. If the current tranny dies find someone else to rebuild it

When you say rebuilt, do you mean that they were rebuilt at a transmission shop. I only ask because some people can rebuild a transmission and sell it as rebuilt, but they don't know what they are doing. I live in Kansas City, and have always used AAMCO for my transmission and clutch problems. I wouldn't junk it unless it has alot of rust or frame damage. Chevrolet parts are cheap, especially for a 350 engine. I have had 7 Suburbans from 1978 to my current 1991. The only thing i can think to check is the fluid and the radiator. If the radiator isn't flowing correctly where the transmission fluid is running through it. It will not cool the fluid and if the fluid is getting hot enough to burn, the clutches can slip and that could destroy a transmission.

did you replace the torque converter is fluid flowing properly? did you flush out transmission lines before starting? I've seen a friend change his transmissoin 3 times because he didn't flush his lihes and radiator trans fluid inlet and outlet holes. always flush out lines,coolers,and check for kinks in lines. hope this is helpful.