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[MiniTruckDX]

hi everyone I am new to this forum and I have a few questions.

First here is my tuck and mods
'90 'YOTA Mini truck DX
Stock 3.0 (for now)
K&N filtercharger
Downey Headers and DOwney 2.5" exaust modified due to lift kit.
Perma cool oil filter relocation kit
Jacobs Ignition system (waste of money)
BAttery relocated to the bed
Superlift 4.5" lift
Downey Torsion rods
Every thing from the frame down has been rebuilt (still need backing plates)
Stock gears and 35" BFG MT's
Warn Hubs

Here is the problem:
I have a weird stumble a low rpm/ crusing speed. It seems like the truck is choking; I mean when I am crusing @ 50mph fourth gear my tack is reading about 2500 rpm and i get the stumble. So iI take my foot off of the gas then resume normal pedal and it is good for a while. When I am winding her out I have zero problems or pinging. Oh yeah if I let her idle for 5 min she will start chocking like she does when crusing.

Here is what i have done:
Timing Dead on
Changed spark plugs hot and cold
Zero vacum leaks and a fresh tune up 1000 miles ago .

Here is what I am thinking:

The resonator that went to the air box brok so i bypassed it .
Could the extra/ air movement to the Air Mass sensor be the culpret?

My exaust has no CAT could it be that I dont have enought back pressure?
I tacked on a 2" tail pipe on the 2.5" exaust to create some BP and to quiet it down some (that Downey exaust is hella loud)

I've had this beast for six years now and up untill now I have no problems. at all.

Any one have any ideas?