imahemi

in my 93 K1500 4wd 305 the heat has been acting up for a little while now
heater hose routing on mine... out rear of intake into heater core then out of heater core to top of pass side rad
the engine was heating up almost to redline (250ish) then would cool down to normal (205-210) but I am barely getting any warmth from any of the vents (floor, dash or defrost)

I started to troubleshoot it by replacing existing tstat with a new 195 one.
that didnt help the situation it does stay cooler now heats up to around 215-220 i think then cools down to about the 195-200
next I changed out the rear outlet as it was badly corroded (mainly just for piece of mind)
again nothing changed.
next I changed the heater blend door actuator... seemed like it was working better but still not running me out of the truck.
now its like its back to square one

I have checked to make sure it is full on coolant and I do NOT hear it "gargling inside" as it had in the past...
my windows dont have that sticky fogging either like the heater core is going out


next thing I was going to do was to back flush the heater core and hope that works...

any other ideas?