I am thinking about plowing snow with a 1990 GMC 2500 - 350 V-8 - 4 x 4 - Suburban. It has a TH-400 transmission in it. I have been searching the web for the transmission operating range, seems everyone has different opinions. Am I correct in assuming that the normal operating temperature of this transmission is between 175 - 225. Normal operating range at about 210 ? I have installed a transmission cooler and fan, and a new Glowshift digitial guage.