1999 Dodge Caravan engine stutter, hesitation

We have the base 4 cyl model.

After driving at highway speed, the van will heistate (shudder) when we let off the gas (e.g. exiting, or slowing for a curve or traffic).
It does the same thing when we go up a hill.

It seems that once it adjusts to the new speed, it is okay.

Turning off the A/C doesn't seem to alleviate the issue.

We took it to our local mechanic who didn't find anything and performed a std tune-up (in desperation I think). This did not fix the issue.

Any ideas?

Thanks, John