Bless: in an earlier post you talk about an Clark CMP 25 having the same issues after you rebuilt the tranny. Is this C500 the same unit? Also what lift capacity is this unit. C500 only means the design series not lift capacity a complete model number like C500-Y50 (for a 5000 unit pneumatic tire) is more meaningful and a complete serial number is also helpful as it contains a lot number which identifies any design changes and year of manufacture. This info is stamped on the truck data plate. If teh data plate is missing the full serial number is stamped in the frame - generally near the RH front drive tire. Also the grade of the ramp is nice info - see my response on your CMP-25 issue.
With this info. you can get a more accurate response.