Disconnect battery wait 5 minutes then touch positive and negative cable on car together for few seconds simple, it will power down everything so everything restarts works in few cars nowadays had to do it not long ago on friends Mondeo when remote wouldn't talk to car after battery change.
Plus one on modulation before you do anything else, I lowered the idle on my P38 when I had it from memory it's just a case of lowering the number in the idle speed box.
Planet rock has moved over to dab+ (only station I listen to, had to buy two new portables one for garage other in kitchen) don't know if that's got anything to do with it but never know.
I changed the oil in the GM box when I had td6 using the genuine LR oil and the box was never the same after, even put a recon valve block in it and more oil change but didn't help so I would say leave it alone if it's working ok .
Don't bother with the foxwell (got one and it won't do recalibrate suspension it might do the sas but don't count on it never tried it on mine) that's why I went for the gap in the end.