That sounds like good advice. The next question on my mind would be, is the transmission slipping and causing this, or is it the engine. I did some research for you and posted the results below.
Can you get a sense on that. It's possible if the torque converter is going on (they do, and transmissions do)..
I transmission oil change (Lifeguard 6 only) might be worthwhile, albeit expensive. Maybe it is possible to haven an analysis done on the oil, at the least. Depending on where your troubleshooting leads you.
Engine Surge/Vibration at Constant Speed LA303-017 Discovery 3/LR3.
"A customer may report a concern that a mild engine power surge or a mild vibration similar to an engine misfire can be felt at certain (not all) constant road speeds. The noise may also be described as a noise from auto transmission (scrape or chain noise in all gears). This noise can be induced by revving the engine in neutral (N) and the pipes to/from the fuel filter will be seen to vibrate. In some cases, diagnostic trouble code (DTC) P2292 'Injector Pressure Erratic' can be logged in the control module.
Cause: The fuel filter pipe connections have been incorrectly connected (during vehicle build or during maintenance and repair), which results in reverse fuel flow through the fuel filter element (large pipes crossed), or cause high back-pressure in the high-pressure fuel pump (small pipes crossed). If the fuel tank air-bleed and high-pressure fuel pump return via the fuel cooler is crossed, the resulting pressure fluctuations cause the fuel pipes to vibrate, leading to the above complaint."
The issue with the A/C May be the Control lever - Recirculation flap or some other flap. Drop me an PM if you want the manuals.
Ok, next step is the self test for the AC I don't think this tests for low freon, but any car shop should be able to check / top off the AC.
With ignition off press and hold the ECON & RECIRC buttons whilst turning ignition on (no need to start car).
The control module will then compare the current HEVAC actuator motor positions with the values stored in the module and will indicate an error by flashing the ECON LED.
If there are no errors, the LED will go out and the system will function normally.
To confirm that there are no errors, turn the ignition switch to the OFF position, then back to the ON position.
Observe the operation of the programmed defrost LED.
If there are errors present, the programmed defrost LED will flash and the system will attempt to calibrate itself.
Where are you located?
