vg30dett stuttering around 5000rpm

Just had engine swapped a couple weeks ago. It only has around 35,000 miles on it. Could the problem be that enough fuel isn't getting to engine or just bad gas. Hopefully the turbos are allright Also yesterday I noticed a clear hose was hanging down behind the driver's side headlight. It forked off into two pieces at the end, what is this tube for. I am guessing it is for the over flow for the radiator. Please help.