98 GT misfires in 2nd and 3rd between 1.5k - 2.5 k RPM

[Chiper91]

98 GT misfires in 2nd and 3rd between 1.5k - 2.5 k RPM when holding throttle constantly. If I floor it through that range, it will be okay.

Things I've replaced:

Air intake:

MAF
Cleaned the throttle plate
Sealed a few leaks in the cold air intake tube (or whatever you call it)
Replaced the air filter.
Replaced the IAC ( it was leaking and causing bad idle), helped with the idling issues

Ignition:
New Coils
New Wires
New Plugs

Fuel delivery system: Had low fuel pressure at the rail (19 at idle), after replacing the fuel pump, went up to 37 PSI
New Fuel pump assembly
New Fuel filter
Have not touched the injectors

Sensors:

New upstream 02 sensors (had a cod for one of them, helped clear the code)
New engine temp sensor as it seemed to run better through the RPM ranges when the car was warmed up
TPS

How it all started:

One night I went to a car show, parked as usual and turned off the car. When I wanted to leave, the battery had died (everything was switched off), my buddy jump started me and I was on my way.
A couple of mins after leaving, it started misfiring. Back then it felt as if the drive belt was stuck and pulling on the engine (the belt was okay, I just never experienced misfire before)
My car kept dying on me until I reconnected the battery terminals, it seems that either of them was loose).
Prior to the incident I replaced the AC compressor and recharged it. While working on the car, I would sometimes disconnect the battery, and after reconnecting it, my car would drive normally for a while and then it would start misfing? Electric issue?

 

[08GT500]

Hi, The Charging System alone can explain most of the issues you are experiencing...
When the Battery is disconnected, or any Voltage drop to the CPU causes supply less that 12VDC, such as during cranking..or Jumpstarting, the CPU loses acquired information it acquired specifically by your Driving habits, it’s sensory input, every CPU adapts to the varying needs specific to its own, independent scenario.
It needs only to be Driven to re-acquire this, Generally needs a few, or sometimes several Miles to relearn & function properly again. If at any point Voltage drops below 12V, you’re back to square one...
I’d suggest you Solidify your Charging system. Alternator output, Battery State, or high Resistance Connections within. You mentioned suspected “Binding” occurred of Belt driven accessories. If there is any Mechanical drag, the Alternator will not provide its necessary output & load the Motor excessively, creating throttle hesitation or poor performance.
Charging System, ‘To Do’s’:
1) Pull your Belt off, verify free movement of all Accessory Pulleys. Inspect Belt for Cracks or Glazing, Replace if necessary (“Gatorback” Belt).
2) Take your Alternator and Battery to Advanced Auto, or another that can measure Alternator Output and Battery response to load. It’s free.
3) Inspect and replace any connectors, clean connections and use Dielectric Grease or Anti-Ox on all connections, clean Battery Posts & Clamps with a Terminal cleaning Brush.
4) Verify Grounds from Battery to Chassis, Chassis to Block, CPU Ground, etc..are all intact and Solid.
Additionally, the TPS has been replaced, Or did you just clean and reinstall, and you adjusted the TPS output to the required Voltages at Idle and WOT?
Has the CPU thrown any CEL’s?
Cheers! John