My 04 F150 ran beautiful until I go the transmission swapped last year. First thing I noticed was the engine would just die on me at some random time for some reason very irregularly. So it wasn't something I could take back to the shop and show them what was happening b/c i couldn't make it happen on demand (i tried).

So i bought a ODB2 meter and have been running it watching RPGs. I feel like it's an RPM problem but i'm not sure.

1. It only happens when decelerating such as to take a turn or a stop sign
2. Turning has a high chance of making it happen especially if i'm in a parking lot , slowing and taking a left then a right without putting my foot on the gas to generate power makes it happen pretty reliably now. However it has happened just going straight and coming to a stop. It even happened on the weekend stopped/idling and changing into reverse. So i suspect the increased power drain of the power steering along with the RPMs dropping just kill it.
3. If i have like the a/c on and i'm idling, there's not enough power to keep the a/c running. It'll come on for a bit then the engine will shutter and sound like it wants to stall then i get warm air for a bit then the cold comes back.

Today i made it happen in a parking lot, the problem is getting worse now such that i can at this point almost make it happen at will with rapid turns and not adding any gas just coasting basically. I notice everything is goovy if the RPMs stay in the 400 to 500 range when slowing down to a stop/turn. And it can go days where that's where it sits and it's ok. But for some reason the RPMs drop into the 300/200 range and then the power steering gets stiffer (less powered) when turning or it just trips the kill switch and the rpms drop to 0. engine light comes on but there are no error codes being logged to look at.

So I dunno at this point. None of this happened before the transmissions swap. And i only just now got the ODB2 meter and able to read the RPMs digitally in realtime.

When i first told the shop about it they thought it was the alternator but the battery charges and all the electrical seems to function fine so I don't think that's the problem but i dunno. I feel like it's something related to how far down the RPMs drop when stopping and for some reason, sometimes they go well below 400 and set in motion the potential for a stall depending on power demands .