Is a heart rate of 140-150 an acceptable heart rate for a 5 year old with a fever of 102.5 and cough? He's taken mucinex and albuterol 2 hrs ago.

Yes. Expect an increase of 10-15 BPM for every increase in 1 degree Fahrenheit from normal .Albuterol will also increase the heart rate by a significant amount as long as it is in his system.The numbers you list are well within the expected and well tolerated at his age.
This is an. acceptable HR for a child with these clinical signs but is pretty hard on the little one. Reduce the fever as much as possible. If the heart rate remains elevated when the fever is down then you should take him to be evaluated by a health care professional.