Honda600rr420

I just bought a 86 rx-7 non turbo this weekend. Im already in love with the car ive always loved rotaries and have always wanted one. But i have a problem when i let off in 1st gear and in 1st gear only it shakes ungodly but only wwhen the car has been drove for a little bit not when it is cold.. The car has a brand new clutch and a brand new flywheel which elimainates that. I replace the transmission fluid along witht he diff fluid to see if that whould help it but no such luck. The yoaks on the driveshafts are good? The only other possible thing could be the transmission u joint/ yoke that connects to the drive shaft. Has anyone had a similar problem if so please let me know i want to fix thsi problem before more problems develop. All feedback is much appreciated.

Honda600rr420

please help me with my problem

Jpk3200

Give people at least 24 hrs to answer your question. This topic has probably already been posted on this forum.