ok, i am/was planning on forkedups first trip to the water (running, in the 3 yrs) being this friday, i have a 1/2 day at work, so i need to set total timing, install drive shaft and splash shield, fill with gas. got home tonight, pulled it out of the garage, fired her up and........no oil pressure, zilch, nada, nothing, zero, gauge didn't even pretend to move, turned it off and shit my pants, ok clean pants and think about this for a minute, used to have oil pressure right?, i cannot 100% say so, i do not remember 100% checking the gauge, i checked the top end, removed valve cover and had oil (then) started it once again, maybe just bled off, ran for about 30 seconds and nothing still, checked oil level, good, oil looks good, nice and clean, check connection at sending unit, seems tight, ground wire to sending unit, gauge pegs at 100, run to checker and buy a new sending unit, install and go to start motor, once key is turned to run position the oil pressure gauge pegs at 100 and stays there. start motor and pressure drops to 25psi, so i have some sort of pressure. no matter what rpm i put the motor at the pressure stays at 25, wtf, i know it has a high pressure pump in it, but it has been three years since it has run, what should i do next, this is freakin me out, i do have 10hrs on this motor with no trouble, stored inside and covered, sealed while paint was being done, flushed oil 3 times before initial start up, running 20w50 mobil 1 right now, getting ready to change again till this happened, using gaffrig gauges, what am i missing, please help my dumb ass

please help my third baby
