Worse when cold? Unless you bought a clearwater head with mech lifters (what you usually get when you order a non-jet valve head) or a caravan head from a junk yard, you have hydraulics. Rev to 3500 for 10 seconds, and kill the switch without taking your foot off the gas, OR remove the valve cover and replace the lifters, AND use a stock oil filter and the above suggested oils. Too late to shim the relief valve spring in the oil pump, unless you like major surgery...

Not responsible for advice not taken...