95 Rodeo Overheating!!!

95 Rodeo, 3.2L Overheating. I just replaced the Thermostat and Heater Core. I ran the truck for a few weeks with the heater core disconnected. Noticed it overheating every once in while. Replaced it yesterday and drove it today, started overheating with in the first 10 min on the road. I turned on the heater and it was blowing HOT HOT air. I would accelerate and let off and once the needle on the temp gauge hit the (H) it would start blowing cool air. then drop back to normal with in a few seconds. Got the truck home and the radiator hoses were hard as rocks. I figured the antifreeze would be gurgling in the over flow bottle but it was not. My radiator cap has a pressure relief lever on it. I flipped it up and steam started bellowing out of the radiator. NO fluid just steam. so i released all the pressure in the system and started it back up with out the radiator cap on. It ran for a few and then spit out some fluid every few minutes. I replaced the cap again and it started to heat up, so i released the pressure and it dropped back to normal as soon as i did that. Thinking that either there is a air pocket or maybe my radiator cap is bad. It also will not suck any antifreeze out of the over flow bottle. That is why i am leaning toward the Radiator Cap. HELP!!! what are your thoughts.
Current Rad Cap relives @ 16 lbs of pressure; is that correct??

Thanks for reading, Chobes

Most folks that chase over heating problems fix them by replacing the radiator (typically it is the last thing they replace).

I was hoping it was not going to come to that and it isn't. I replaced the Radiator Cap and when the engine started getting hot it would relase steam. but that was only if i had the overflow bottle disconnected. I noticed the the part of the woverflow bottle where the hose from the radiator connects was almost completely closed off. So i drilled out the hole and it started working. The radiator also took a gallon of antifreeze. Didn't realize it was that low. Any how all is fine now.
Thanks for the post.

Wish I'd seen this earlier. Sediments can clog the outlet at the bottom of the reservoir. Anytime I do cooling system maintenance, I clean the reservoir. As soon as you said the system wasn't drawing fluid from the res, I figured that was your problem.