Why on my 2004 GMC Envoy XL the shifter doesnt engage to reverse when i start it up?

[Ace of Spades]

I depress the brake pedal but it doesn't go in reverse? Then it seems to catch or latch on and it shifts in reverse. This only happens when I park car and try to start it up again.

 

[Molson02536]

I depress the brake pedal but it doesn't go in reverse? Then it seems to catch or latch on and it shifts in reverse. This only happens when I park car and try to start it up again.

Not sure what you are describing. If the shifter does not move in to revers and stuck in park while the brake peddle is engaged then releases a few seconds later. Your shifter lock interface needs to be addressed and most likely needs to just be adjusted.

If the shifter moves in to revers position and then the transmission shifts in to revers a few seconds later. Slow, slipping or no reverse: “lo-reverse” clutches are worn out, fluid leak in the reverse apply circuit, or broken sunshell. It is possible to remedy a fluid problem by removing the checkball from its cage in the case in the rear of the trans may help (must remove valvebody), or adding a seal restorer product. May also have worn boost valve (can replace in the pan).

Put a line pressure gauge or visit a local trans shop and on the pressure test port, 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 0.490" boost valve stock is 0.470" boost valve(easy fix in pan).

Good luck and keep us posted.