i believe the 90 has a closed system. if so, check the return "T" fitting going to the pressure bottle. my 89 closed loop had an over heating issue and i replaced everything, even installing a grand cherokee fan clutch. still had the heating issue. i then removed all the hoses to check for clogs. when i got to the little "T" fitting i noticed it wasn't allowing coolant to flow into the bottle. when i went to clean it it was totally clogged. i couldn't figure out why it wouldn't unclog when i tried pushing something through, well not until i noticed the tiny factory hole. it is no more than 1/8". once i unclogged that tiny hole, the system worked perfect. on a hot day in stop and go traffic i cant even get it to reach 210 degrees. problem now is that i may be running rich since the ecu is being told it is running too cool. so before you replace all those expensive parts, clean out the system first. unless of course you know those parts need replacing. by the way, i am running a used radiator from an 87 that looks to be factory.