2003 Town and country low power and low MPG

Mileage should be 18 mixed use, over 21 highway 70mph or less when using cruise control to get transmission turque converter to lock out, 19 if using your foot.

If transmission was changed at other than Chrysler dealer (suggested by the narrative wording) they will have used the wrong ATF with a modfier that is half the price and claims it is compatible. The transmission will work with the wrong ATF, but the performance and reliability suffer. (The transmission flush machine at an oil change place is also unlikely to be loaded with ATF+4.)

Verify fluid levels are correct. Transmission is checked with transmission hot (drive 10-20 minutes), with brake applied engine running cycle PRNDL through all selections pausing a few seconds at each, put transmission in Park, leave engine running, check level on tranmission dipstick using "hot" scale. Fluid is added or removed through dipstick tube. Use only approved ATF+4.

Suggest 1st look at missing or broken engine vacuum lines, dirty air filter, PCV valve, dirty fuel injectors, gummy throttle plate, gummy intake manifold. Suggest correct vacuum line faults, replace air filter, replace PCV, 1 bottle Lucas in tank, 1 can intake spary cleaner for throttle plate, 1 can Seafoam spray for intake, will also clean cylinder carbon from valves due to ethanol fuels. If improved and was not dirty air filter or PCV, then change brand of fuel, EPA minimum for injector cleaner does not overcome ethanol gum in these engines.

If not improved suggest 2nd level fixes are spark plugs and wires, then O2 sensors. It takes a lot of work to get to the rear spark plugs, a cylinder leak down test for engine compression is best performed when changing the spark plugs. This test should also be able to isolate any comprression leaks as gasket, valve, or ring.

Suggested 3rd tier check is intake manifold gasket(s).

Check for frozen calipers,e-brake sticking. clogged cat/or ****.