My "4 wheel steer" message lights came on when I was on the freeway. The rpm wou on 2002 GMC Sierra Denali

Wouldnt climb past 2000 rpm. I gave it some gas but still wouldnt past the 2000 mark. The truck hasonly 123000 miles on it. Is it my tranny thats going out or a bad sensor? Or is it that it has 305/40/22 wheels?

Asked by for the 2002 GMC Sierra Denali
have all codes scanned and post so we can adv