i have a diablo predator programmer. when i take the diablo tune off and go to the factory tune i get a late , slow, harsh, shift from 1st to 2nd. this is a normal take off

when i put the diablo tune in it goes away.

also when i have the factory tune on the transmission does not seem any thing like it did when i first got the truck. it feels like it is sluggish, crazy shifts, does not want to downshift sometimes

another thing is the transmission starts off in 2nd gear sometimes. this is not a all the time thing. once in a while it will do it.

ive searched and nobody seems to have had these problems

any ideas, fixes....
2003 ext cab, 5.3, 4l60E, 40,000 miles

 

could be

 

I had the problem with my transmission starting out in 2nd sometimes. I don't know the cause and since I just blew my transmission I never will. I didn't have any of the other issues you descibed though.

 

Do to the fact that you are having a 1-2 shift problem and also second gear starts at times. I would be looking at the 1-2 accumulator circuit. It is possible that you have a cracked 1-2 accumulator piston. Along with that you could have a broken spring in there. With the factory tune the line pressure could be lower and this condition might be more noticeable. Bad part is that your 2-4 band is probably hurt.

 

I had a similar problem, mine didn't want to upshift to 3rd until above 2500 or 3000rpms. Turned out I burned up some of the syncros due to removal of tq mgmt from tuning. But it was covered under warranty.