not all code readers can read psd's,so even if you have to take it somewhere to check for codes have that done.most auto parts stores readerss wont work.my tranny had a shift issue where it seemed like it wouldnt shift outta first until i released the throttle a little,then it would shift.well actually by paying close attention (and the help of a ford diesel tranny guy)we figured out it was starting out in 2nd gear,and it wasnt a first gear issue.BUT my tranny also threw codes regarding shift malfunction and incorrect gear ratio.so i rebuilt my valve body using sonnax valves,(shimmed up a little),replaced the line press mod valve with a sonnax .427 and she shifts clean and smooth with a nice firm shift.so long story short find someone(delar,tranny shop,friend)who can check for codes and start there.also,make sure your fluid is full and not BLACK....GOOD LUCK