1998 Subaru Legacy Intermittent Engine power problems

Intermittently my engine will have trouble getting the car moving. I'll slowly let the clutch in at regular rpm's (round 2000-3000, whatever feels right) and the engine will just stall, or will lurch forward repeatedly at like 8mph without me moving the clutch. Generally I pop the clutch out, knock it up to 4000 (way higher than I usually do) and slowly let the clutch in, leaving me with burning clutch smell.
I find this usually happens after I have been driving for a few miles, and generally not at the start.
Also, the engine temperature gauge usually has the needle just barely off the peg. Sometimes the temperature rises to half way or so, but sometimes I'll go miles without it rising. When I drove from Utah to Colorado, it read completely cold the entire time and was unable to heat the cabin.
What can I do to help the intermittent stalls and the cold engine?