If you were driving it before you found this out and had no problems then it's most likely okay.

 

Did you get the proper sending unit? One is for a gauge and one is for a light. Don't know if the wrong one would cause your gauge to read incorrectly or not.

 

20/idle 40/driving is absolutely fine. Your gauge is probably reading correctly now. Often a failing pressure sensor (which you had) reads too high.

Lifter tick in a 4.0? Yours is the first I've heard of.

Heh. Just kidding. My '99 did that when it was new. My '96 started at about 50K and still does it at 230K. It's just characteristic of the 4.0, IMHO.
No reason to worry unless it gets progressively worse.

 

Yea, that was my thinking too, but as Radi points out; maybe the gauge is reading correctly now.

Yup, got the gauge version.

Good to hear that 20/40 is ok, I'm not used at seeing the needle below the center line.

As for the lifter tick, yea, I'm more annoyed than worried about it right now – will do an oil change to 10w30 and see what happens. Maybe order some of that mystery stuff from the states, but I'm not a big fan of putting additives in the oil.

 

MMO (Marvel Mystery Oil) is way better than an additive this stuff was used in airplane engines durring WW2 and beyond, as I have learned. Most the people that use it swear by it, and it can help with the lifter tick.
been using it for 7 years now bought my 90 with @248,000 now at 425,000..... always have had the tick, doesn't burn oil. (maybe it helps who knows?)

 

If the lifters are sticky or partially plugged, it'll help. If they are just worn it won't.
Nice thing about MMO is that it either helps, or it does nothing. I've never heard of it doing any sort of damage, unlike certain other oil additives.