Help please
 

I've been driving my truck the last couple days and it's been running a little weird. When i first broke it in a few months ago it ran really fast as soon as it started. Now it takes like 5 minutes at full throttle b4 it starts to run at top speeds. Then it seems like it runs faster then it did when i first got it. IDK is my engine going?

I messed with the mixture and that doesn't seem to help.

Thanx
Freak