07 Tranny problem

[jml]

1st and 2nd shifts fine but when it goes into 3rd or Drive it rives up but will not move,the engines rives like its in neutral?Could there be a selinoid or switch problem? Thanks guys for your help Im not much of a tranny guy.
This problem just started all of the sudden,no noises or signs of shifting problems.

 

[Molson02536]

1st and 2nd shifts fine but when it goes into 3rd or Drive it rives up but will not move,the engines rives like its in neutral?Could there be a selinoid or switch problem? Thanks guys for your help Im not much of a tranny guy.
This problem just started all of the sudden,no noises or signs of shifting problems.

Visit a local trans shop and have them put a line pressure gauge on the pressure test port and go for a drive to verify proper line pressure. Base pressure at idle in P,N,OD should be around 70psi and around 140psi in R. Max line pressure should be at least 190psi at WOT in 1st or 2nd, 225psi is optimum. If base pressure is low, trans or pump is worn out. If max pressure is low, check EPC solenoid. If reverse is slow to engage, and line pressure does not come up to at least 130psi in reverse, replace the boost valve with a Transgo 0.0490" or 0.500" boost valve (easy fix in pan). http://www.sonnax.com/instructions/HP-4L60E-01-IN.pdf

No 3rd or 4th gear: “3-4” clutches are worn out. R&R. The car is safe to drive (in 2) until you can get it fixed or No 2nd or 4th gear. 2-4 band is slipping. Servo seals may be damaged (can be fixed without removing trans. Otherwise, 2-4 band is worn out. R&R.

Regardless, bring the Sierra and they can hook up a Tech2 scanner and they can determine from the scanner what issues the transmission has that needs to be addressed.

Good luck and keep us posted.