340 engine / oil question

The only modifications were , new aftermarket oil pan, rocker arms, push rods, lifters, intake,carb,hedders. And like I said before, the new pan is allmost 1/4in shorter than the one I took off. That's why I thought that it maybe, be that the oil pickup is right on the pan ,and not alowing enough oil to be pumped to the top of the engine. What do you guys think?