What could be the problem. Stalling when trying to change gear.

What is your question?

My 2006 Chevy Colorado has 132000 miles and is a great truck but recently usually once a day it feels like it doesn't want to shift gear. I start up let it running for a minute and then leave for work, when I press the gas most mornings the rpms stop rising and it tops at about 10 mph, takes a minute and then it kicks in and drives just fine the rest of the day. I'm hoping this isn't a transmission problem any ideas on what it may be?

What makes this problem better or worse?

Nothing really makes it worse usually does this once a day at least.

How long has your 2006 Chevrolet Colorado had this problem?

It's been a few months