overdrive flakiness and check engine

[limodrivr]

Hi. This question is buried in another reply, so Ithought I'd ask it up front:

Current problem withthe 97 Grand Marquis(4.6 v8) 99,000 mi:
Check engine light comes on, later changes to continuous blinking; mechanic fixed a 'wire' (spark plug?) but problem came back.
There would be an occasional slight 'miss' to the engine, and
the exhaust seems not as clean as it should be.
In the middle of that ('check engine' temporarily not a problem), the trans started getting flaky in overdrive between 45 and 55 m.p.h. It seemed if I would accelerate very gently in that range I could avoid the 'kickiness' in the overdrive.
Also, turning off the overdrive would stop the problem, obviously.

Looks like 2 problems, but with electronics being what they are,
could these be related?

Any suggestions would be appreciated.

Hal