I have a 99 Suburban k2500 4x4 with 213000 miles on it. I am having problems with the transmission shifting. I have to let off the gas to get it to shift, and when the transmission downshifts it slips and revs up until I let off the gas a little to let the pressure off and then it goes into gear. I ran a computer diagnostics and it says the shift solenoid is bad, the code was PO751. Has anyone had this problem before or knows where the solenoid is to change it.