Nissan Stagea feels like its running out of gas all the time white spark plugs

hi, well its been a bit of a mystery its started cuting out a bit and surging while driving along like the motor wasnt geting enuff petrol. so we changed fuel filter and pump was alright for a couple of days then started doing it again so bad that it ceased the engine and all the oil feed lines were blocked so we got a newer fresh motor out of a r33 skyline and chucked that in. it went really well for about 2 months then started to do the surging thing again. all coil packs are working well. so checked the spark plugs and they were white so gave them a good clean and put them back in and took it for a drive. when the car heated up it started doing it again. Please help im almost gonna give up and take it in 2 the shop but really really dont want to!