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Just tried to start a build, using PLA, extruder stepper started slipping like the nozzle was plugged. Started over, rethreaded the machine, fed filament manually to purge the hot end, and material came out like normal. Started the build again, nothing extruding followed in a half minute or so with the stepper slipping/clicking again. So I put my temp gun on the nozzle and it says 125C, where the system says 210C. I have never measured this before, could someone tell me if it should be 210 with a temp gun on the tip if the systems says 210? I replaced the resisters and thermistor a few months ago, I'm guessing if there's a problem it's with one/both of these?

The pickup area of the temperature gun is probably larger than the hotend and won't read accurately. The sure fire way to tell the temp is with a thermocouple. Lots of multimeters come with them, including a $20 one at Harbor Freight. That's what you'll want to calibrate your thermistor readings with.

Unthread the print nozzle slightly, clamp the thermocouple between the brass and the aluminum with your fingers (don't break it with a tool), and give it another reading.