My 2007 avalance will not engage into 1st gear in the D or 3 position, but it will engage in 1st gear in the 1 position and 2nd gear in the 2 position. I have worked on cars over the years but mostly Fords, I checked the line pressure at idle and in all forward gear ranges plus park and neutral it is about 65 psi and 90 in reverse position. I have a snap on modis scanner and there are no codes. According to the mitchell manual line pressure matches the pressure control solenoid amperage. The shift solenoids seem to match mitchells chart. That is about all my knowledge gets me and am not sure where to proceed from here. Any help appreciated.