blower works, but the heat only gets to about 75 degrees. max. does this sound like a heater core?

 

I removed my heater core last summer (to lose the weight associated with it...hoses/clamps/core, etc)
Mine didn't work all that well to begin with.
When I removed the dash to repair/install things, some of the foam that is there to help prevent air from bypassing the ducts and heating/cooling your dash was obstructing the duct and (i assume from the heater) had formed a mild plug, not completely but enough to obstruct flow.

Id recommend checking the pressure coming out of the vents when your AC is on, then again with your heater...if there is a significant difference, then you may have an obstruction. Also check the marriage of the hoses to the body at the firewall (2 hoses right next to each other) I too mine out rather than repair it since I live in southern CA. You can look forward to a couple hours removing the underpanels/knee bolster bracket/lowering column and removing the dash, id definitely recommend getting a spotter on this one, i did it alone and it took a good 2 hrs to align the dash again to put a couple bolts in to hold it. Nothing easy about doing the near splits in dickies in a so CA summer alone trying to support a 75 lb dash with a shoe, a telescoping rod, and various other items.
good luck

 

Living in Western Canada, I can sympathise

From long experience, here is my advice. If the heater core is gone it will usually leak and drip onto the passenger side floor. If not, it might be getting plugged. But try replacing your radiator cap first. Believe it or not, a leaky rad cap can keep you from getting decent heat from the heater.

If none of that helps, try one step hotter on the thermostat. If there is still no joy, then replace the heater core.

 

Another sign that it is the heater core is if the windshield keeps fogging up inside. That is due to the leaking coolant evaporating through the vents and condensing on the inside of the windshield.

 

Another tip is to scrap the heater switch that is controled by the climate controls. The heater switch only lets coolant go into the heatercore when you have the heat or vent switched on. The old school way is to just bypass and rip out all that crappy heaterswitch stuff and just let the coolant run through the heatercore. It works for me and it really cleaned up the engine bay. If you want to know how to do it go to my website, I have a simple tech article.

 

If you have a 160 thermostat you can easily have this problem on a cold day.