1998 dodge ram van it starts fine but when you put in drive or reverse and start to stalls out now had just replace the plugs air filter what would be wrong with it?

A 1998 Dodge Ram van stalling when you put it in gear, even after replacing plugs and air filter, points to a problem beyond simple maintenance. The issue is likely related to the transmission or something affecting the engine's ability to handle the load of driving. Here are some possibilities:

* Transmission Issues: This is a strong possibility. A failing torque converter, low transmission fluid, worn clutch packs, or a problem with the valve body inside the transmission are all potential culprits. When you put the van in gear, the engine is suddenly under load, and a weak transmission system can't handle it. Check the transmission fluid level and condition. Low, dirty, or burnt fluid is a major red flag.

* Crankshaft Position Sensor (CKP Sensor): This sensor tells the engine's computer where the crankshaft is, which is crucial for ignition timing and fuel delivery. A faulty CKP sensor can cause stalling, especially under load.

* Throttle Position Sensor (TPS): This sensor tells the computer the throttle position. A faulty TPS can lead to incorrect fuel delivery, causing stalling, especially when the engine is under load from driving.

* Idle Air Control (IAC) Valve: This valve regulates air flow at idle. A malfunctioning IAC valve could cause the engine to stall when it needs to increase RPM to handle the load of driving.

* Fuel Pump/Fuel Delivery: While less likely given the starting issue isn't reported, a weak fuel pump or clogged fuel filter might not provide enough fuel under load, causing stalling.

* Vacuum Leaks: A vacuum leak can disrupt engine operation, causing stalling, especially under load.

Troubleshooting Steps:

1. Check Transmission Fluid: This is the most important first step. Check the fluid level and condition. If it's low, dirty, or burnt, you likely have a transmission problem.

2. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any trouble codes stored in the vehicle's computer. These codes can provide valuable clues about the problem.

3. Inspect for Vacuum Leaks: Visually inspect all vacuum hoses for cracks or disconnections.

4. Test the CKP and TPS Sensors: These sensors can be tested with a multimeter or by a professional mechanic.

5. Have it Professionally Diagnosed: If you're not comfortable troubleshooting these components yourself, take it to a qualified mechanic. They have the tools and experience to properly diagnose the problem.

Don't continue driving the van extensively with this problem as you could cause further damage, particularly to the transmission.