My motorhome (1990 460 V8, 77,000 miles, good UOA on 4400 mile Maxlife 10w30) has a mechanical oil pressure gauge I installed. In about 10,000 miles it works fine. Sunday we took it on a 200 mile trip. For some of the time on the first half of the trip the oil pressure gauge would flutter, but the needle remained centered on the normal pressure. At 2000 rpm in OD it fluttered over about a 5 psi range. So I downshifted thinking to knock out the flutter and it started sweeping a 12 psi range at 2700 rpm. The gauge would stabilize and then go back to fluttering. Hadn't driven the motorhome in 7 weeks (nor started it). After a 2 hour stop at the destination I headed home and there was no more flutter. What could have caused it?