2005 grand prix help engine problems

[traveus]

when i cold start my car it'll run fine until it gets hot then it runs rough nd the trans will start shifting hard. i have a check engine light on for gas cap and thermostat. it also only gets hot when I'm driving it. it'll cool down when parked with ac on. the broken thermostat usually kept the car cooled down cause its stuck open but now that its summer time and its like 90 out its not helping. hottest it ever got was bout to 2 lines from the red lines nd it was acting like it wanted to die. fluids are all full. no oil in the coolant. just got to 170k

[Fivefingerdeathpunch]

I'd replace the thermostat before you overheat it and do some damage.

If the car runs fine at normal OP temps then that will be good.

[traveus]

it don't run fine at normal temp tho. the broken thermostat kept it at half the normal temp and that was fine until it got hot out. I'm going to replace it just haven't really had time and wanted to figure out whats going on with my car.

[qroberts16]

Start with replacing your thermostat and cleaning the maf. Sensor

Sent from my VS986 using Tapatalk

[traveus]

replaced the thermostat today and same thing is happening. the old thermostat still looked good too.