I need some help, I own a 1996 B3500 van with a 5.9 liter and it broke down on my son in Kansas and he said that it's getting misfire codes on almost all cylinders except for two. He said that it was a sudden change in power and it felt like the transmission went out because he had to gear down to get the van to move, I drove up there from TN and checked out the codes. It is misfiring but the transmission seems fine. I will be going back up there to work on it on 4/7/2017, someone told me it might be the catalytic converter but I'm at a lost and was hoping for some guidance and what to check for when I get there. I have no way to tow it and this will be my only shot to try and fix it. If I can't then I will have to call scrap yard and I really would hate to do that. So if anyone can help I would definitely appreciate it. Thanks

 

Do a full tune up and a compression check.

 

This link has some good info I think and there's more... based on certain symptoms you may find the fix quicker hopefully... I also had recent misfire codes on cyl. 6 and 8. I'm no pro mechanic (not even close) and posted a thread here a few days ago for help. Before having to delve too deep I found it was my 2 spark plugs causing the misfires.

http://www.justanswer.com/dodge/5klk...-cylinder.html

I agree with jkeaton, start with the simple stuff like ignition... especially if you know that a tune up hasn't been done in over a year or 2 or 3 or it's been driven more than 20k like me.
Pull some of the offending plugs and take a look for odd corrosion, burnt looking etc. Check the gap (mine was 40 first installed and 50+). Clean them up if showing normal wear, but at $2. or so per plug may as well go with new. Have new coppers ready to replace and new brass distributor cap and rotor, and maybe plug wires. Make sure the wires are routed correctly according to this TSB
http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm
Coil could also not be providing required spark so keep an open mind i guess..
Could be other things like vaccum leaks, egr, injectors, mechanical and so on, compression test will help narrow some of that down

there's lots of youtube videos and threads to help begin to diagnose misfires, try googling -1996 dodge 5.9 multiple misfires- or use your own wording, so you can get a plan for it based on your symptoms and prepare.

Good luck and wish you well