GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hello the fact that this is an intermittent problem and you can get it to reset leads me to beleive it may be an electical issue, on your transmission if it lost all power down to the trans its default position is second gear regardless of where the shifter is. I have had several do what you are describing and the most common issue was beleive it or not ignition switch, Get you a voltmeter check the voltage on both sides of the trans fuse, you want it to be near battery voltage and if you have tilt wheel jar the wheel up and down turn it and you may see voltage drop if it gets below 9 or so volts the solenoids lose power and bam your in second
i understand, and do you have the 4l80e? If so I would still check the voltage at the fuse please trust me it will eliminate that as a possibility and it is very common. Have you scanned for any codes in the computer
Good morning, no i dont know of an underdrive. Your truck most likely has the 4L80E couple of ways you can find out one the pan on the trans is it square? If so it would be a 4L60E which i doubt if not it would be the 80 those were the only two automatics used.
The speed sensors are another frequent problem but usually will drop u to second if they fail, and you are reporting no pulling at all. Do you have a code reader to scan for codes
sir we are perfect for each other i to work strange hours I will be looking for your reply thanks