engine cuts off @1800rpm, '03 GT

[bluecorners]

My '03 GT has a number of common mods, but I think my issue revolves around the use of my Diablo tuner. The problem is that at about 1800rpm the engine cuts out momentarily. Lets say at 1800 it cuts out and at 1810 it comes back and continues on normally. Its almost as if there is a blank space in the computer program at that spot and the engine hesitates because it is not getting instruction from the computer. I have put the Diablo program in and out over the years a couple dozen times at least and am wondering if maybe that has caused some of the necessary parts of the FORD program to be altered. The "stumble" seems to happen whether or not the Diablo program is in, so I'm thinking somehow the FORD program has been compromised in an area that the Diablo does not address.
Anyone have any ideas about what might be going on??

[MorePowerMike]

First issue.. Diable.. Sorry but I'm an SCT Dealer and that's that.

but since the problem remains when the tune is not installed. It's probably not the tune's fault.

I'd check mechanical stuff like spart gap, is it a misfire? Are any check engine lights coming up?