hi all, i have a 96 gmc with a 5.7 vortec and as of late it don;t idle right, its ok in park, but once in gear, it jumps to about 1100 rpm then slowly comes down to about 800 rpm, until you drive over 30 mph then the idle will only fall to about 1200 rpm. i replaced the iac valve and tps with new ones, i searched for vac leaks and found none, i have put new plugs, cap & rotor on, with no change in idle. no lights on the dash, no stored codes. ***? it was somewhat tollerable on dry roads but now the roads are covered in ice so it really sucks now. any input is greatly apprecieated and thanx in advance!