I have a 2006 Ranger 6x6 with a 700 efi engine in it. Recently it has started bogging and backfiring when hot, seems to happen mostly at a moderate RPM between idle and accelerating. I've read through a bunch of forums of people with the same issue but no luck so far. Below is a bit of history and everything I've tried.

The issue definitely only happens when the engine is hot, when starting cold or if I let the engine cool down for 30 minutes I can drive at 30-40km/h 2km and then the issue starts again, the longer I keep driving it the worse it gets. Let it cool for a while and its good again. I am not getting the high temperature light and the radiator is blowing hot air so I believe I am cooling ok.

I formerly had issues with the charging system, the harness to the ECU had melted on the 3 cables that charge it. I ended up cutting off the harness and using stake-on connectors to reconnect each cable, this was a year ago and it has been fine until now, I did recheck all the connectors and they all seem fine. I put a multi meter on the battery and measured the voltage to make sure it wasn't dropping when the issue happened, voltage is steady at 14.4ish

I checked the boot between the throttle body and the cylinders, no damage and boot is still nice and flexible.
I also checked the hose between the air filter and the throttle body, again seems fine. I checked the connections to the tbap sensor and tried to see if the wire was broken as suggested in other posts, seems to be fine.
I pulled the air filter which was dirty, I don't have a spare right now so I vacuumed it and blew it out, I don't believe its the issue as why would temperature affect that,
I pulled the fuel injectors, I don't have any cleaner with me but the looked pristine. Would temperature affect these?
I pulled the spark plugs and checked the cables, I know the cables are only a couple years old as one was broken when I bought the machine 3 years ago, I also pulled one cable and a time and ran it on one cylinder to make sure each was firing consistently (this helped me diagnose my snowmobile last winter so I tried it again). I don't really know how to tell if spark plugs are bad. Could my symptoms could be spark plugs?

I looked at the connection to the throttle position sensor, again everything looks ok, I'm leaning towards this possibly being an issue as the problem seems to be at a repeatable peddle position where it bogs. If I go past that position it starts running ok, and if I back off it runs ok. This was while in neutral so no load, when driving it does seem to happen in a wider range of pedal position depending on loading.

I'm running it on new premium gas, I know it doesn't require premium but I get premium for the boat so that's what goes in all my small engines. I added a little seafoam to the gas today and drove it 10 km, doesn't seem to have helped although not that much will have gotten through yet.

I would appreciate any suggestions of things to check or try.


Edit: Thought I should mention this machine is used mostly on gravel roads, the most it has driven through since I got it is water that didn't even come over the floor. Its usually parked under a roof however it has been rained on several times although not recently.