i have a '08 chevy malibu and the heat only kicks in after you go past 40 mph and when it does its not very warm air. what could i do, what could it be?

Thermostat...195 degrees~ warms up in a couple of minutes, will open up and allow Hot coolant into the coolant loop~

if you ran without it...you'd never come up to temperature~

ok, next question is it hard to install, could I do it on my own or do I need to take it to a garage?

Also may want to check anti freeze level if it is low could cause your problem.

all the fluids are good, we took it to a local shop. they first checked the antifreeze level, then got in my car and turned the heater on and off, then told me they don't know whats going on and to take it to a different garage. I was just checking to see if its something I can change myself before I go and pay an arm and a leg for something I could do on my own.

two hearty bolts with an extension ratchet...might want to clean the mating surfaces...on a scale of 1 to 10...I'd rate this a 3 on the level of difficulty~

You could do it yourself depending on how much mechanical include you are. There could be some videos online showing you how to change thermostat.