Welcome to the forum
What year is the replacement 3.0l?
O2 sensors read oxygen levels in exhaust
High oxygen is .1v, which is Lean
Low oxygen is .9v, which is Rich
If a cylinder misfires then no oxygen is burned/used so when it is dumped into the exhaust manifold O2 will drop to .1v.
So rough idle would show O2 voltage swinging around.
Computer normally runs idle rich, and ignores O2s at that time, which is why you see the .7 at times,fuel trim at idle will normally be +5 to +8
The +20 fuel trims can also come from misfires, same as above, but while driving the computer adds more fuel than at idle.
After engine is warmed up let it idle and unplug the IAC Valve, RPMs should drop to 500 or engine may even stall, either is good, it means no vacuum leak.
If RPMs stay 700+ then you have a vacuum leak.
Watch MAF voltage or set reader for gm/sec, Grams per second.
At idle you will usually see 3gm/sec because it is a 3.0l engine
Voltage at or just under 1volt
But what you are looking for is steady readings for either, no jumps or drops if RPM is steady.
Raise RPMs up and hold it steady at 1,500, 2,000, 2,500, 3,000
You are watch for steady reading, the actual number is not as important as the steadiness of it, if it jumps around replace MAF