Greetings! 1999 GMC Sierra Z71 with 233,000 miles

I have been chasing continual problems with P0171 & P0174 bank 1 lean and bank 2 lean codes that only occur when it is below about 35' F for the last year. Recently had was driving at 65 mph on interstate with cruise control on and vehicle suddenly lost power, but cruise was still on. Engine was still running but when accelerator was depressed it seemed to do nothing. If pedal was pressed to floor engine would cough and act like it was backfiring. Pulled over and shut down while waiting for someone to come pick me up which would take about 30 minutes. After about 15 minutes waiting decided to try again. Vehicle started fine and ran like normal at 65 mph for about 20-25 miles then problem reoccurred with no SES light or codes set. Shut down and let sit 5-10 minutes and able to continue another 20-25 miles. Able to do this about 3-4 times to make it home, on last leg noticed using scantool monitor mode that when vehicle lost power two of the oxygen sensors went to 0.0 volts. Remove oxygen sensors for troubleshooting, during removal threads damaged due to galling, so replaced all oxygen sensors and catalytic converter Y pipe for same reason. After this work, vehicle ran fine for 2 1/2 to 3 weeks. Then problem reoccurred again with same results, able to limp home by stopping and letting set for 5-10 minutes each time. On last leg noticed on scantool monitor mode that when problem occurred that fuel loop 1 and fuel loop 2 showed open indicating computer was controlling fuel using engine temp, MAF, and throttle position instead of oxygen sensors. Currently cleaning all grounds on vehicle and checking for clean, solid connections on PCM. My question is if there is any procedure to test PCM other than having GM dealer go through troubleshooting chart with Tech II? Any info would be appreciated. Thanks!