Good afternoon. I have a '94 Suburban with a 350 motor. Changed the t-stat and bypassed the rear heat. I'm guessing I have a major air lock going on. It takes forever to get any movement on the temp gauge but if I hold 1500 rpm it will get to 195 degree. Heat is lukewarm at best. As i drive the temp goes down to around 140. Rad and front heater core are a year old. Everything worked fine until I bypassed the rear and changed the t-stat. Twice. Anyone have any thoughts? Thanks.