Silverluv, Had a reel lift valve on a N-Series doing the same thing. Put all new o-rings,poppets,seats,etc. in valve and still experienced the same problem. Plumbed a gauge in reel lift hose port and run combine,slowly pressure would start to build and in about 5 min. had a 1000psi pressure showing on gauge. Finally had to replace valve due to internal crack. Hopefully you will find something simple stuck to poppet or seat. Sometimes by cleaning end of poppet and stretching spring a little will solve problem. Good luck, Hyper Harvest II