Can someone please tell me the conditions that have to be met for 3rd gear TCC apply in a 2001 Blazer. Just trying to understand it. Sometimes I have 4th gear TCC but no 3rd gear TCC. Other times I have both.

Is it temp related? Seems to have 3rd gear TCC but only only on my way home from work since the weather turned a bit colder. Been trying to drive with shifter in 3rd because TCC applies at lower speed in third gear and I drive a steady 40mph on these roads. Never seem to have 3rd gear TCC unless gear shift is manually put in third. At 40mph resulting RPM in third gear is significantly lower than 4th gear with no TCC - but only if TCC locks up in third. Just can't figure out why at times no third gear TCC, yet does have 4th gear TCC if I shift into drive and speed up to 47mph. Reason I worry about getting it to hook up in third is gas mileage at the speed I am normally driving.