Ralph77

I think you drive it for awhile and go get it tested in the Jeep.
And while you are at it get your battery tested again too.

lawsoncl

Nobody has mentioned belt tension which might be letting the alternator pulley slip under load. Intermittent not charging would not likely be the PCM, as that would usually just outright fail.

mervebitanem

It is actually a voltage regulating circuit located within the Powertrain Control Module (PCM). The EVR is not serviced separately

lawsoncl

I would also stick my meter on the field coil connection on the back of the alternator. One side should have constant battery voltage, and the computer controls the ground side of the field coil. The computer actually switches that ground on/off rapidly to control the charging current/voltage. Measuring with a meter on DC should show is averaging low and close to zero if the PCM is commanding high output. Connecting the ground side of the connector to battery ground should kick the alternator into full output.

I'm thinking you've got a weak alternator or a wiring issue. Did the problem start with a new alternator? The Oreilly's test isn't conclusive for many problems.