The cars a 1995 camaro z28, heres the list of problems..
now for the story, my dad was driving the car and noticed it was really overheating (but never dangerously) so he let it cool down for 30 minutes, then dropped the top and turned the heater on high and inched it to firestone to get looked at. they said that the water pump needed to be replaced. my dad didn't trust firestone so he took it to another mechanic and the mechanic said that the thermostat needed to be replaced.. after fixing the thermostat he said he found out that that a cylinder head was bent or cracked and it was probably caused by the car dangerously overheating for 30-40 minutes (im positive this never happened) and he wants 2 grand to fix it, so i just really need some more experienced opinions on this so if you can offer any thanks

also.. the car runs perfectly fine except for the problems i mentioned, no weird sounds or anything

 

does anyone know what the problem could be

 

If you have a warped head, you'll either have coolant being consumed through the combustion chambers (white smoke out the tail pipe), coolant in the oil (oil looks like a milkshake) or a small coolant leak though the combustion chambers resulting in a slow consumption of coolant and you need to top off the radiator. Do you have any of these symptoms?

 

"Underreving" is usually due to not havng the rear end gears you think you do.

2.73 in place of 3.23 would account for the 20% difference. Or 3.42 instead of 4.10. That's pretty easy to check.

An improperly calibrated tach could give the same results.