I am in the process of purchasing a 1990 Ultrastar with what someone told me was a "Wonderful" 454 Chevy engine. It has only 54,000 miles and the vehicle appears to be in very good condition. I have one concern. When I have taken the RV for drives each of the last two days the engine has no power for the first half hour, except downhill and the oil pressure gauge is hitting FAR Right, above 80 psi while we struggle to go up inclines at 40 mph. Then on cue, 30 minutes into the drive the pressure guage settles at 60 psi and we move along at 55-60 mph, sometimes passing cars and only the steep, long hills cause us to drop into the 45 mph range. Is this typical for this type of engine or do these symptoms sound familiar to anyone and are a sign of something about to go wrong or is going bad at this time with the engine? Any education on how this "wonderful" engine works, suggestions on how to shorten this warmup time or parts of the engine to have a mechanic review would be greatly appreciated.