Not sure larger injectors without increased air(turbo) will do anything but set Rich codes
Computer bases air/fuel mix calculations on fuel pressure and flow thru stock injectors
It "knows" XX fuel will flow out of a stock injector if it is open for 100ms(milliseconds)
And thats what it bases 0 Fuel Trim on
If XXX fuel flows from a larger injector then computer will have to decrease open time of the larger injectors to get 14.7:1 ratio, if it has to reduce open time more than 15%(-15 fuel trim) then it will set Rich code
And you will still have flat spot
Not sure what the silencer is that you removed??
But if you got the flat spot after removing it then my guess would be removing it caused a turbulence in the air flow or vacuum at the intake ports so less air/fuel mix flow into cylinders for that moment, flat spot.
Generally speaking fuel pressure dropping issue would effect high demand first, i.e. driving up a long hill or sustained highway speeds, dirty fuel filter would be most common cause for this.
But it wouldn't cause a flat spot until vehicle was at higher speed, and it wouldn't be a "spot" it would be a limit, can't go above it.
43psi with vacuum hose off means pump is probably OK.
If you raised RPMs to 2,500 or so and held it there for 30 seconds with no slow drop from that 43psi then I would say pump is fine.
And yes, if it was 34psi and went to 33psi when you opened throttle plate then vacuum INCREASED for that moment in the intake, and that would cause a flat spot, so I would look at vacuum in intake as symptom causing flat spot, not lack of fuel
Your Ranger uses 90lph fuel pump, and it works for 2.3l turbo'ed Rangers, same 90lph pump was used on turbo'ed T-birds.
TPS(throttle position sensor) is more like accelerator pump than vacuum line on FPR.
TPS voltage gives the computer the "heads up" to add more fuel instantly when gas pedal is pushed down.
Using MAF only would be slower to react and cause a hesitation, flat spot, when throttle plate is opened.
If "silencer" was near MAF then removal may have changed air flow thru the MAF making a longer delay