The HF compression tester is actually OK. Obviously for professional use you'd want something better, but for the occasional home user it's fine. The 90 deg elbow for testing in the glow plug hole will fall apart, replace it with a JIC fitting from your local hydraulics shop. A well stocked auto parts or farm store may have it as well.

Add a chunk of clear tubing to your fuel return line, see if you have air in your system.

Have your injectors pop tested and rebuilt if necessary.

Check delivery valves and seals, look up the delivery valve thread. I chased "runs like crap when cold runs better but still poorly when warm" symptoms for years, came down to delivery valve seals.

__________________
617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap