Problems with my truck

I have a 96 chevy k1500 I just replaced the transmission and last night the spark plugs I pulled them out one at a time to make sure I didn’t get them switched up but it will idle just fine but as soon as I drive it down the road it has one hell of a back fire and won’t stay running please I’m up for any suggestions and help I’m moving out of state soon and need to get my truck running!

When my pickup backfired it was because the mixture was too rich, a consequence of the choke not working. I don’t think it’s the transmission. That it idles properly should mean you have the spark plugs attached correctly.

I know it’s not the transmission it’s a brand new one from monster‘s transmissions.com I did plug-in an O2 sensor that wasn’t plugged in all the way I might have it plugged into the wrong one So I’ll check that too and the spark plugs make sure they’re connected properly