starts out third gear

I have a 2000 zr2 blazer that sometimes it starts out in third gear. When I drive for a and stop for a short time(15or say 20 min.) an not all the time it starts in third.If I stop and start again it usually starts in low gear. Thats the only time it will to it until I stop again for 15-20 min. I have look in the books and all I can think it might be is the vcm not getting the right signal from the transmission fluid temp. sensor? If thats true would that tell the torque converter the wrong info.Thanks for any help

I have a 2000 zr2 blazer that sometimes it starts out in third gear. When I drive for a and stop for a short time(15or say 20 min.) an not all the time it starts in third.If I stop and start again it usually starts in low gear. Thats the only time it will to it until I stop again for 15-20 min. I have look in the books and all I can think it might be is the vcm not getting the right signal from the transmission fluid temp. sensor? If thats true would that tell the torque converter the wrong info.Thanks for any help
Any check engine lights on or flashing?
How many mile on transmission and when was last transmission service?
How is fluid and fluid level?
You need to get it put on a Transmission/engine capable scanner and read out data and codes.
Post back any codes.