I have a 2001 Dodge Durango, I just changed the catalectic converter, the truck acts like it isn’t getting any gas, when I drive it above 65 mph for 20 miles, but I can pull to the side of the road for a min or two and go again, it keeps doing this. I can drive it all day in town no problem. Comp. says misfire on 1,2,&4. any thoughts thanks

Start by telling us how many miles are on it, what type of maintenence has been done. If you continue to drive with the misfires you will be replacing the catalytic converter again real soon. You need to find the cause and fix the misfire. The spark plugs and wires should be replaced if they are old.

You need to determine if the misfire is caused by the lack of fuel pressure is secondary ignition problems. Inspect the spark plug wires, drive the vehicle with a fuel pressure gauge connected and monitor the fuel trim levels with a scan tool.

Concur w/the above advice, determining what’s causing the misfires is job 1. The three most likely culprits are weak or missing spark, incorrect fuel pressure, and low compression. If I had this problem the first thing I’d probably do is measure the intake manifold vacuum, might provide some clues and is easy & quick to get the measurement.