Engine misses & backfires

Hey All!

Kind of a long story here so I'll try to shorten it up as much as
possible... sorry if I miss a crucial detail... just ask if you need
more info...

1999 Chrysler Sebring Jx Convertible - 2.5L V6 with 102,000 miles. I
bought the car used at 65,000 miles for my teenaged daughter.

When purchased the car got around 17 mpg. I had a tune-up and the fuel
injectors cleaned and mileage went up to 24 mpg.

Mileage stayed stable for awhile then started dropping around 95,000
miles. I had another tune-up with plug wires replaced (this past
January). Car ran fine but at only about 21 mpg.

In April the engine started missing horribly and I took it to a new
shop (I had moved from Fort Lauderdale to Atlanta, car was trailered
up). New mechanics said the wrong plugs were put in and the plug wires
were oil soaked and needed replaced. I did new plugs, wires plus a new
distributor cap and rotor button (another $450).

Car ran great for about a week and then started missing again, I took
it back to the shop and they found a defective plug, replaced it and
the car was running good again.

Now, three weeks later the car is missing horribly, backfiring
especially at low rpm's. I took it back to the shop and they said the
plugs, wires etc. are fine but that the oil is not draining from the
heads back to the oil pan and the hydraulic lifters are not
functioning properly so the valves are not opening and closing when
they should and this is causing the engine to backfire and miss and
that I need to have the heads reworked. (I'm no genus but this sounds
like utter BS to me.)

I believe the car has always had a barely perceptible miss... at idle
you can watch the rpm guage jump (and not just when the fan comes on).
Mechanics who've hooked the car up to a scope tell me I'm nuts.

There is no check engine warning light. The one time it came on it
was reset when the mechanics in Atlanta replaced the plugs and wires.
It has not come on since. (I have run the diagnostic on the
instrument panel and the check engine light (all lights for that
matter) works great.

This problem does not occur when the engine is cold. After the engine
warms up however its very noticible on acceleration and when the RPMs
is under 2000. At 50 mph, and 1800 rpms up a slight hill with no a/c
you'd think you had a transmission problem the way the car jerks and
lunges. Dropping the gear down or accelerating and the missing and
backfiring goes away... once the ride stabilizes out to crusing speed
(70 mph) you can feel the missing again but you can't detect (hear)
any backfiring.

So, now I have a car who's engine misses so much its hardly driveable,
new plugs, wires, cap and rotor.

Suggestions?

Phil