I had the same issue w/my '90 3.0, and was concerned w/how low it was when at idle and at 3k rpm's, so I installed a set of after market gauges for oil press., water temp, and an A/F gauge. With the new gauges the oil pressure was right where it should be. Like others have said it is likely just the gauge, no oem gauges other than those on high dollar cars are going to be that accurate.

With the rebuild it is likely that Toyota just replaced those parts that were covered under the HG warranty, unless you specified otherwise.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed