Bad Miss when cold only

Hey Guys
New to forum, been reading all night and need some help!! My 2000 blazer was running great untill I changed my radiator last weekend and cleaned my MAF. Since then, the truck has a horrible miss on steady cruise 45-55mph and shift points are much higher rpm than nml. No SES, no codes, all fluid levels fine. Again, truck ran fine before I changed rad and does this only for first 10 min of driving each morning. Any time after that, truck runs and shifts fine. Please help!!

What engine and mileage?
How is the tune up secandary ign?
How many mile since last tune up?
Good AC-Delco plugs?
Is the check engine light flashing when it does it?

A good engine capable scanner will give you a lot of info on what is going on.
Even with no check engine light any codes will be in history or present or past codes.
Read out all sensor readings and fuel trims and miss fires past present and history and check camshaft retard readings.
Also a good fuel pressure check may show problems.