Shifter lever won't return to the " center " position always. The problem is intermittent and seems to occur more in the heat. I've heard there may be something binding the mechanism. Nothing is apparent. I hope it's not an internal issue.

Follow the shifter reach rod that runs from the shift lever back to a short lever on the transmission. Take the nut off and take the rod loose from this short lever. Then, move the forward like you are going to shift into low gear but don't actually shift the transmission into gear. Feel for the spring tension. Then, move the lever backwards and feel for the spring tension there. Check the shift lever and the reach rod for binding. If you don't feel the spring tension trying to return the lever back to the center, it's likely that the shifter pawl return spring is broken. This spring is what returns the shifter lever back to 'center". But,the temperature of the transmission will not change this. If the spring is broken, it's broken cold or hot. If the spring is good and there is not bind in the linkage, the problem may be in the shifter cam mechanism inside the transmission. Either way, this is an internal issue in the transmission.

Good Luck
steve

This is likley the pawl spring in the transmission taht is broken.