After many upgrades, I decided to have the rear end replaced with a used one that was in better condition. Same 373 ratio and all that stuff. The car was running absolutely smooth before the change. The rear end was sloppy though. The mechanic installed a rear end out of a Volvo wagon, maybe a 82 or so, along with IPD adjustable Panhard rod and adjustable IPD torque rods. The vibration was very bad. took off the IPD panhard rod and torque rods and things were much better. But I still have a vibration, mostly under load and felt in the seat of your pants. Before the rear end switch, I had replaced all the front bushings, the front and rear springs, the rear shocks, the front struts, the rear trailing arm bushing. All was smooth with no vibration. After switching the rear ends, and getting rid of the IPD torque rods and panhard rods, I replaced the transmission mount, the motor mounts. The drive shaft had been balanced and all ujoints replaced before the rear end switch. But I still have this vibration. It's not bad but it sure is annoying. I'm completely out of ideas.Help
Jim