I originally had a problem with underextrusion when I got the printer, which I solved by putting a nut in the extruder to increase the tension of the spring. It worked well but a plastic extruder is simply a piece of shit at the end of the day, so I ended up upgrading it.

Here's the thing: I installed a new metal extruder and calibrated it in quite well and got to printing. Then, something happened. Whether the nozzle got clogged(I think this was an issue at the start, but is no longer) or whatever, a print of mine failed about two hours in due quite clearly to underextrusion. I tried recalibrating it, and then cleaned out the extruder/hotend assembly and put it back together, but the problem has somehow not only gotten worse but less predictable too. Changing estep doesn't matter, or doesn't really affect the problem, nor does changing how tightly screwed in the extruder arm is, which I've found can have a big effect with a metal assembly.

Any advice? I really can't figure out a reason as to why this is happening anymore.