I have a 1992 Ford Bronco with a 5.8L 351 Winsor and a E4OD Trans; Recently the CEL came on but it would only stay on at idle or under 2k RPMs. It has since then got worse and now shifts hard under 2.2k RPMs and idles high when in park; 1.1k RPMs. I have been told that it's a vacuum leak and have went through just about every vac line on the motor with no success. I don't have a smoker/fog machine to test to see if it could be a minor leak at the air plenum but I can't hear or see any signs that it I feel would cause such harsh shifts or idling issues. I know it's not the TPS because if I disconnect it the RPMs change and the CEL stays. About a year before this I had a similar issue with the "EGR Sensor/Tube from the Exhaust Manifold to the Air Plenum, but I had a trusted shop fix it and haven't had issues until now; It's also partial EGR deleted/Smog Pump Delete. I've been told there are vac lines that run to the trans but can't locate them. I also had front and back ring and pinons done with posi; Although I wouldn't see that screwing it up unless there was a vac leak at the 4x4 Hubs. Any advice on how to tackle this problem would be appreciated!