I have a 1986 IROC, Canadian spec with no tpi or other electronics. Fitted a T56 six speed "kit" gearbox with Spohn crossmember and driveshaft. I cannot get the driveshaft balanced (two tries cost more than the new driveshaft) and have a persistent deep buzz at about 60-70 Mph or greater.

Spohn won't answer any emails.

Any one had problems getting this combination to balance??

Otherwise good improvement from old T5 box.