Hi XXXXX. Thank you for asking your question on Just Answer.
-How many miles are on your Suburban and what type of engine (size) do you have?
Thank you again for trusting us with your problem. Please reply as soon as possible so that we can finish answering your question.
Hi XXXXX.
You have done most of what needs to be done, but based on the miles you have put on it, the radiator may have some obstruction in it, even if you have flushed it out.
Does the air coming off the radiator feel really hot when the engine is up to temperature? In other words, does it feel like the radiator is doing a good job?
There could also be a problem with the flow of the coolant through the system, such as maybe a failing water pump.
Here is a check list of things to investigate, just in case I missed something. It is a PDF file that you should be able to view on your computer or print out.
Engine Overheating
Let me know what you find or if you have more questions.
Take Care, Greg A.
Hi again,
Here is another little note I found concerning your vehicle.
Engine Running Hot, Overheating and/or Loss of Coolant (Polish Radiator Filler Neck and Replace Radiator Cap)
1999-2000 Passenger Cars and Trucks with Composite Radiator End Tank Condition
Some customers may comment on one or more of the following conditions:
Cause
The radiator filler neck may have an imperfection in the sealing surface. Correction
DO NOT REPLACE THE RADIATOR.
Using a piece of 400 grit wet/dry sandpaper backed with a flat piece of wood, polish the filler neck sealing surface using a circular motion.
Replace the radiator pressure cap with a cap of the same part number as shown in the GM Parts Catalog.
Master Troubleshooter
Working with Electronics & Cars for 25+ Years