99 Blazer 4.3l overheating problems

I'm having some interesting problems with my Blazer....

I've been working through the cooling system problem and am in the process of flushing out the orange (and associated gunk) to switch to the green stuff. However, I'm also having other problems and I'm not sure if they are related....

Symptoms:

1) Heater blowing cold
2) rust and stuff in the coolant
3) heating quickly, then overheating (esspecially with the A/C on)
4) Engine cools VERY slowly
5) Oil pressure is sporadic (ranging from 20-50 on the gauge).

The issue with the oil pressure is only happening after the engine is heated. The pressure changes in direct porportion to the RPMs (low RPM = low oil pressure, high RPM = high oil pressure).

I've just found the article on flushing the colling system (99-06-02-012D) and will do that, as I'm sure that is one of my problems. However, the oil pressure and the fact that it heats so quickly and cools so slowly make me wonder if my oil pump is going out or gone....

Any thoughts, or am I completely off base?

Regards,
Jacob

Follow the procedure exactly!! No shortcuts. When you are done with the flushing before reassembly remove the heater hoses at the core and either use air or water and backflush the heater core by itself, it's plugged like the radiator and thats why it is blowing cold. Do not under any circumstances get this crap on you, it stings and smells really awefull. If its really bad you may want to do it twice.
After this is done worry about the oil pressure, I'd change the oil first and see where you are at. 20 to 25 at idle is not unusuall, think my 01 is at 25. If the coolant is gelled the engine has been using the engine oil to cool it and probably has thickened it at this point.

Well, here's the thing. I've already flushed the system twice using the Prestone back flushing kit and water. I placed the T in the heater hose and supposedly it will back flush the heater core as well, as long as you run the heater at full blast during the process. It this correct?

As of yet, I have not used the cooling system cleaner, removed the bolts under the blazer (where are they located?) or flushed just the heater core. Considering you stated to follow the procedure exactly, I guess this would be best. So I will do that.

I'll try the process and get an oil change and see where it gets me...

Thanks for the information.

Regards,
Jacob