Started a couple of weeks ago, under power the speedo is accurate, but let off the throttle and it drops about 20 mph. If i push the clutch in it reads within a couple of mph of the under power reading. Seems that the biggest drop is only when decelerating without touching the clutch. Does the speedo gear in the transmission slip if the yoke is loose?
-RATCHET-

 

I think i would start with making shore the speedo gear,adaper(if used on your truck) and speedo cable tip isn't rounded off!

 

Check the bolt that holds the slip yoke on the out put shaft of the transmission, if it is still a Getrag. If this bolt is loose your gear will slip and speedo will read wrong. Also cruise control will bounce, jerk, well you know .
GW

 

Checked nut on transmission yoke today. It was flopping around in the yoke. New seal, new fluid and speedo is back to normal.
-RATCHET-