odd TBI problem

[MonzaRacer]

Actually yess you can, tap into the pressure line with proper fittings(ie compression or flared fittings and run a proper braided steel/teflon lined hose with crimped on ends to a guage, mount guage on cowl or I believe Autometer had a membrane device that fuel pressure line ends at then another filled with no flammable liquid goes to guage.
OR use electric low pressure guage as the TBI is only running 13 psi max.
IF its dropping you may need to do away with stock tbi regualtor if possible and use aftermarket one.
You also may be having computer over heat so maybe a computer case fan blowing on ecm may help, had a dragracer that lived in Phoenix with similar issue, he eventually went Megasquirt.