[Roadsters] Jumping 4th

[DeWayne Reichert]

Long story I'll try to make short.
  We've had our roadster for a year now and it's time to get it summer ready. I've rebuilt the brakes, replaced the bearings, put in longer front studs. But I still have one thing left to fix. My 5 speed transmission  jumps out of 4th gear. The guy we bought it from said he had it rebuilt and it looks like it (new paint and gaskets) It shifts fine no grinding or forcing it into gear. But you put the power to 4th and out it jumps. Any ideas or thoughts before I tear into it would be great.
   
  Thanks 
  DeWayne & Jeanne
  68, 2000
  SRL - 311