I've got a 90 Formula that has developed a vibration around 65mph. The driveshaft was balanced(supposedly)after installation of new U joints. The problem was cured for a while until it started again. The vibes seem to originate from the rear of the car and it has improved since the weight that the first shop installed was removed from the rear end of the shaft. My question is could anything suspension related(wheels,bushings,etc.)be causing this? No bulging or distortions have been seen on the tires to suggest a tire problem and no wheel weights are missing and no bushings seem to be out of sorts. Could anything in this area be causing this?

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Mongoose-NCTGA-1990 Pontiac Formula/305 TBI-700R4 with Edelbrock Performer TBI intake,TES headers,and STB,K&N,MSD-6AL,Holley laser shot coil,Accel Extreme 9000 wires,Jet Stage 2 chip,TCI shift kit with corvette servo,Richmond 3.73 gear with Auburn 3 series posi,high flow cat,SLP 3" cat back,Eibach sportline springs,Energy Suspension poly throughout,Lakewood LCA and adjustable panhard bar package,SSM subframe connectors,IROC wonder bar,Tokico 5 way adjustable struts and shocks,Autometer electric fuel pressure gauge,Alpine,JL Audio,MB Quart,92 GTA taillights,92 GTA aero wing and hatch,Steve Spohn LCA relocater kit and torque arm,MacEwen White face gauges,84 T/A cold air induction air cleaner,Grant Formula GT wheel.