4l60e shift problem

[willboivin]

97 Yukon 5.7 has 119k. 4L60E transmission and was allways smooth and perfect then it would not shift into 3rd, its like it goes into neutral. I slow down some and it kicks back into 2nd. I've read alot of forums on the 4l60e so first I changed solenoids and filter, no luck so I replaced ignition switch harness and it worked perfect 1st 2nd 3rd and drive smooth shifting but only lasted about 10mins,4-5 miles down the road then right back to same problem. Codes P0740 P0753 P758 and P1860. I've checked the #20 fuse and have 12 volts there. I'm pretty sure its gotta be electrical and not tranny. Also I've read where someone says to buy orginal factory wire harness and I bought generic one. I'm asking to see what others think, if its electrical or if it is internal transmission problems. Today I'm going to try testing volts at the trans connector, I didn't wanna drop pan again to test solenoids but might have to. Hope someone can steer me closer. Thanks

[Chubbs878]

I have heard of a faulty mass air flow sensor manifesting itself in poor shifting of the trans'

 

This may not apply to older vehicles but worth investigating or replacing the MAF sensor. Next, I would be dropping the pan & looking for cracked or broken accumulators, etc.