Any advice for my wife's '96 T&C Chrysler Minivan that is doing
strange things after replacing blown 3.3L engine with lower millage
engine:

Background:

1) My mechanic is competent and have used him for years;

2) 3.3L engine blew at 135,000 miles and asked my mechinic to
find/replace the 3.3L engine;

3) After much time, found 65,000 mile engine and I said to go with it
since it took so long to find this one;

4) Engine seems to work very well, even better than original;

5) First strange thing that showed up in first 200 miles was that the
front windshield wipers would cycle one time only by itself. I can add
that the T&C did do this when new and it took dealer three tries to
fix which they said it was a bad series of 6-way switch on column;

6) Second strange thing was that the transaxle downshifts by it self.
This is much more serious and also showed up in first 100-300 miles
after reinstallation of low mileage engine;

7) Tried adding "Lucas Transmission Fix" product since the minivan was
laid up for about three months and both my mechanic and I thought it
might be the inactivity causing problems with fairly high mileage
transaxle. However, Lucas didn't help and still have downshifting
problem;

8) My big concern is that I have had one downshift on highway doing
about 60 MPH and RPMs jumped from normal 2300 to 5000. I pulled over
quickly, turned engine off and on again, and was off again with no
more incidents on that specific trip;

9) Check engine light has not come on yet, but mechanic wants to see
if any codes show up, which I'm trying to get done today; and

10) Another observation: problems occur 50-70% of time when hitting
bump which is causing my mechanic and I to think it might be
intermittent electrical connection in one of the engine connectors.

Any advice (keep it clean and constructive, please) would be
appreaciated.

Bob