I agree with GMC . Sounds like a fuel starvation/volume/pressure problem.
You will need a 15 -20 PSI gauge with a good sweep to be able to accurately read any discrepency in a 13 PSI system.
A 60 or 80 PSI gauge wont have enough incrementation for anyone to discern a problem or not.
You can remove the fuel filter outlet line and patch in at that point for your test fitting, it is way easier than trying to hump over the engine and fight the rigid lines in the back of the TBI
been there done that.
For a test and short term operation, you wont need to use Fuel Injection line as the pressure is only going to be 11-13 PSI.
When you get it hooked up, start it run it , then replicate the operational condition which causes the symptom, the watch the gauge to see.
Check the specs for peak head pressure with engine off key on, engine running at idle, and engine running at acceleration( vacuum/regulator test) Good luck.