Holding gears when cold

I’m still trying to learn my Tundra. Is it normal for it to hold gears when the engine/transmission is cold? I notice when I leave in the morning it stays at 2000rpm for a couple of seconds then shifts back normal but this is only when it’s cold. Also I really want to have a piece of mind when it comes to the transmission. It’s a high mileage 07 with a detailed Carfax history. I can see that it has been serviced regularly, for example it has 5,000 mile service and so on. The last service I saw was the 120,000 mile service and spark plugs replaced. Still no specific detail that the transmission has ever been serviced. I had the dealership inspect the fluid last week. It’s dark but has hints of red. I was thinking that I could do a slow method drain and fill. Change the filter, replace pan gasket, drain only small amounts of old fluid and put in same amount of new fluid. See what it does and repeat as needed.

 

Normal

 

Yea I’ve noticed this on 3 different tundras I’ve had. Normally lasts a few miles for me of holding lower gears.

 

I had same deal, hooked in my truck one day when it was about 40 out and it took forever to het out of first. I started panicking thinking my trans was going out but read that if it's not to a certain temp it does this