cant figure out why car keeps overheating

Check for burn holes under the wire harness sitting on the Upper intake plenum, could be the coolant is leaking away through. I had the same problem 3 years ago on a 04 Buick Regal

If you are losing coolant and overheating, the most obvious thing would be the head gasket. Sealants may help depending upon how much fluid you are losing. I have used Barr's Copper Sealant for Intake manifolds on a high mileage Ford vehicle with the 5.4 Triton engine and it worked very well and eliminated fluid losses as well as making the engine run cooler and it doesn't use oil as it did before I put in the sealant. However, the engine never overheated, it only lost about 8 ounces of coolant per day, which was not normal.

If you are experiencing actual coolant loss then follow Indigo's advice. Barr's Sealant works very well and may save you spending more money on an old car. Also are you sure you got all the air out of the system. That's the most common problem with cooling systems that have been drained and refilled. Your car will not cool properly if there is air trapped in the system.