95, 4.9 deville chugs at 45mph after tranny rebuild.was told to change egr and after cleaning tubes, still chugs so till my mech can cleanout intake.egr disconnected it runs ok.for 1/2 hr.then car is horrible no power and motor is noisy. cat was checked. is this egr related?
Yeah a ton of variables here... very hard to say over the internet but one thing that comes to mind is the viscous converter clutch also known as TCC or VCC. It does kick in around 45mph or maybe a tad earlier and can somewhat 'bog' down the motor especially when passing. I actually wired a switch to disable mine because I just dont like the way it feels. Its hard to say w/o riding in your car myself but might be something to mention to your mechanic.
Btw, you say your motor gets 'noisy' 1/2 hour after disconnecting the egr? That's probably because it's pinging w/o the EGR. It's kind of a metallic knocking/clanging sound... yet another thing that's hard to diagnose from behind a keyboard.