Engine trouble ????

[cheyguy]

I've got a problem and I'm not sure what to check next! My '80 4x4 has a 350 w/auto trans that starts fine, idles fine, runs fine till it shifts into 3rd, then the engine really boggs down. I took it to my trusted mechanic who said it was the tranny. Well $2000 later and a rebuilt tranny it still no better. But now when I accelerate above 40 mph or go up hill the engine sputters and revs (like a clogged fuel filter). I've changed the fuel filter, checked all the plugs and wires. I'm thinking I need to rebuild the carb but I'm not sure thats my problem. Any ideas are appreciated. Thanks, Mike