my 2007 ram 1500 4x4 q.c. 5.7 hemi is having a bit of an issue, When I am driving at about 65 mph steady pressure on pedal the rpms are staying at 2000 rpms until I take my foot off the pedal for just a sec. and then apply steady pressure back on the pedal, (maintaining 65 mph) then it settles back down to about 1600 - 1800 rpms. What could this be? I need to change plugs, but would plugs cause this? Any and all help appreciated.