I have a 6CTA 8.3 Cummins with an Allison MD-3060. This is a manual engine with electric tranny and has the cable tps (allison p/n 29506376). It will not shift out of 2nd unless the mode on is displayed. The shifting from 3 to 4 will not occur unless I am going downhill at wot and from then on its smooth sailing. Shifting from 2 to 1 is very hard, if it were not so heavy it would slide the tires. I notice that when the engine brake is on it displays 4's on both sides of the display. I have changed the fluid and filters and has not helped. Code is 21 12, is there a way to trouble shoot the tps to see if it is bad and do you have any other suggestions. Thanks
Allison shifting problems
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