engine

hows ur water pump doin, check ur pully and ur belt for slippage.

also check ur oil pump and pick up tube may be restricted. ur oil cools ur pistons. also ur piston rings should transfer the heat to the cylinder walls and ur water jackets on the other side of the walls will carry the heat away so maybe ur rings r bad.

stuck theromstator blown head gasketor your temp control senser is bad telling the computer it is hot when it it is acutally not,is it boiling over.

Air lock maybe?

I would guess air in the block keeping the fluid from flowing properly, or a stuck thermostat... I know you just replaced the thermostat, but they tend to be pieces of s*** and it's not unheard of for them to be bad before installation. It may be the temp control sensor as someone above stated. I would start by letting the car idle with the rad cap off to see if any air gets out of the system... Simplest thing to try(and free)

Just an FYI If oil pump was blocked to where heat is overcoming a cooling system with new components, then there should be an oil pressure light somewhere. Secondly your rings don't cool your engine(they are a friction point that generates heat actually)

make sure the air baffle under the radiator isn't missing or shot

I dont think its the water pump because it was just replaced with the engine. Its a rebuilt 305. Also it wants to overheat while Im on the highway which is specially weird, cause thats when it should cool off the most. Its never overheated only because I slow down so it wont. Also after running on a hot day pretty hard I checked the overflow and it was "foamy" no oil but it was foamy. Im not sure if its the gasket I hope not but usually you'll find oil in the coolant or other way around. Ive replaced the thermostat twice. Ive had the mass air flow censor changed, dont know if that could make a difference. Please help.....

what is the baffle under the rad??

its not actually boiling over because I wont let it. I slow down when Im on the highway otherwise it would probably overheat.

I just replaced the belt and the water pump was replaced with the engine.

just a simple solution---when was the last time the radiator cap was changed. I had a 87 pontiac gta, it did the same thing and it was just a radiator cap. Also check the air dam mounted in the nose of the car, it deflects air from the ground into the radiator. should be a three piece unit on your model. Although i had an 82 trans am with a 396 big block i installed and it did not overheat, and I had removed the air dam.

also sensors only tell you what is going on in an OBD1 system, would not cause it to overheat. Removing the radiator cap would just cause it to overheat quicker. The function of the radiator cap is to provide pressure in the cooling system lowering the overall boiling point. The more rpm's you turn, the more pressure that is fed back to the cap allowing for release into the overflow container.JUST FYI

check your water pump, and hope you didnt blow a head gasket, if you did blow a head gasket go to a drug store and get some liquid glass and pour it in your radiator you wont have a problem with your head gasket after that, i have the same camaro as yours and mine did the same thing so i sealed it up with liquid glass

try bleeding the air out of the system. an air bubble could be causing air-lock

well first off how hot is it running? tpi systems were made to run hotter than youd think. the fans were made to kick on at like 220 if im right, i had alot of the same problems so i put a new radiator in it and a 160 thermostat and still no luck. also ran direct power to the fan but still no luck. then i got an aluminium radiator out of a gta and my problems whent away my iroc had a brass radiator in it from the factory. also have hit that air dam on drive ways and such and bent it backwords and it ran consiterably hotter. i dont understand why it would run hotter on the highway but mine did the same exact thing.

todds right if the dam is gone or broken air goes up between the radiator and engine with the dam it goes in to the radiator

I'll bet you it was the water pump.

if it aint your water pump believe it or not your radiator cap can mess up and cause your engine to over heat it happend to me on a 92 camaro z28 so if it aint the water pump id check that out its somthing most people would never think of

the air damn on the bottom needs to be intact if not air flows under car instead of through radiator check it out