I have a 81 K5 blazer with a TH350 tranny.Running 4inch lift with 35's It runs good in first and second but when it shift to third(drive) it boggs down. It goes gutless. I can floor it and kick it in to passing gear and it runs fine but then shift to third and gutless again. It runs about 2000RPM at about 60-65 normally now when it hits third it turns 1500-1700RPM. Is this what happens when it starts slipping. Not much experience with autos. I have friends that had trannys slip and they always reved up high RPMs to even move. Whats going on with mine. Can some one shed som light on this. Thanks