My daughter has a 2008 Impala with the 3.5..... For a year she has had the codes for the SMOG pump and check valve...I replaced the SMOG pump but have not changed the check valve....this afternoon she came home and said her display had shown the ubiquitous "Reduced Engine Power"....but it'* intermittent. When I check the codes the codes for the SMOG pump and Check valve were there of course but a new code was the P0651..... Is this related to the SMOG issue or is it the Throttle position sensor on the Throttle Body..... or something else to look at?

This is a voltage reference code. I can't see how it could be related to the smog pump.

The trans may have lost comms and it was sent into limp mode. Smog pump has nothing to do with it.