What causes excessive pressure to build up in the fuel tank?

Looking at the EVAP sytem is a good to check next.. Did you get new solenoids for the system. There are 2 purge solenoids that will get stuck into whatever position they failed in, i.E. Stuck open.
Does gas escape trotu the fuel filler when you open it?

Is the Idle Air Control Valve, IACV, which is sometimes also referred to a the engine Load Sensor, ELS.
This is an electro-mechanical device which idles up the engine when loads such as; power steering, A/C and other accessories or situations call for it.
It can adversely affect the performance of the engine.
It is tough to diagnose problems such as these because electric/mechanical control modules feed from sensors all over the engine and accessories which makes it hard to tell if a sensor is bad, the control unit is bad, an IACV is a control unit that sometimes has integrated sensors, or if the is a problem with the Vehicle Main Computer.

If you're experiencing excessive pressure build-up in the fuel tank of your 1996 Dodge Ram 1500, despite having replaced the fuel pump, gas cap, and fuel evaporator cylinder, there are a few potential causes to consider:

Ventilation System: The fuel tank has a ventilation system designed to allow air to enter and exit the tank as the fuel level changes. If this ventilation system becomes blocked or restricted, it can cause excessive pressure build-up in the tank. Check for any blockages or restrictions in the vent lines, charcoal canister, or other components of the fuel tank ventilation system. Clear any obstructions or replace any damaged components as needed.

Evaporative Emissions Control System: The evaporative emissions control system is responsible for capturing and storing fuel vapors from the fuel tank. If there is a malfunction in this system, it can cause pressure build-up in the tank. Check for any issues with the evaporative emissions canister, purge valve, or other components of the emissions control system. If necessary, have the system inspected by a qualified technician.

Check Valve: The fuel tank may have a check valve that helps regulate pressure and prevent excessive build-up. If the check valve is malfunctioning or stuck closed, it can cause pressure to accumulate in the tank. Inspect the check valve and ensure it is functioning properly. Replace it if necessary.

Faulty Pressure Regulator: The fuel pressure regulator controls the fuel pressure in the system. If the pressure regulator is not functioning correctly, it can cause excessive pressure in the fuel tank. Have the fuel pressure regulator tested or replaced if needed.

Restricted Fuel Return Line: The fuel return line allows excess fuel to return to the fuel tank from the fuel rail or fuel injectors. If the fuel return line is blocked or restricted, it can cause pressure to build up in the tank. Check for any obstructions in the fuel return line and clear them if necessary.