Hey guys! Longtime reader and finally joined to ask a question. Will try to lay it out logically. Have a 1996 4.0. New Jasper long block installed about 6 K miles ago. Here is what is happening:

1) After about 2K miles of smooth sailing, I have been traveling up a lot of mountain passes here in CO and trailering my raft around a bunch. I have noticed that I get pretty defined hiccups, hesitation and stalling for .1-3 seconds under load, usually going uphill, but always on choppy pavement or dirt. The hiccup can sometimes make my tach needle plummet, and I a few times I saw a CEL come on for a split second. It is terrifying when I've got a big rig following on some of these passes! Lose speed rapidly.
2) I do sometimes have some random idle RPM surges around town.
3) I found and cleared a hidden Ford specific P1300 "boost" code. No CEL. 98% of the time the car runs fun, fires up quickly and accelerates smoothly.

What I've changed recently:
-engine
-fuel pump, filler neck, filter, injectors.
-Spark plugs and SP wiring (dunno the brand; mechanic did it), coil pack (less than 10k on it; generic)
-air filter, new carquest MAF sensor

So I looked up the code (really limited info) and saw a few suggestions that were mainly for the F150s.. MAF (replaced), TPS sensor, crankshaft sensor and possibly O2 sensors. It is an air/fuel specific code... but I am boggled as to how I don't see any CEL indicating a misfire or sensor specific code. Reading about the TPS, I do see that it can cause RPM surges and hiccups or stalls. But if anyone has any ideas or suggestions or experience I'd love to hear it! Don't want to just throw parts at it in hope of fixing a problem I don't fully understand. Frustrating because I can't replicate the issue around town, just heading up to the mountains generally.

Thanks in advance!!!

 

...gosh. Read another thread above. I had a big crack in the air filter housing below the MAF. I just went to the junkyard and replaced the housing entirely. Would a cracked housing cause issues like that?