One of my AX5's started making noise in the higher gears first, then got progressively louder in the lower gears as the bearings got worse.
If price and time is a concern like it sounds it is, I'd replace it with an AX5. Too much of a headache to find a transmission that will work with your 2.5L and with an upgraded engine down the road, without dropping a bundle on a conversion bellhousing. If you do the AX15 conversion, you're still limited to what you can bolt in front of it.
I'd go the AX5 route, then later drop in an entire GM 4.3L drivetrain including the 231c, keeping adapter costs out of the equation.