stalling issues

[My F4i]

I have a 69 long bed, just recently had a new holley carb installed on my truck. It ran fine for about a week or two but one day i was driving on the highway and as soon as i took my foot of the gas it began to sputter. When i came to a stop it would stall if i didnt keep my foot on the gas and then became very hard to start. ANy ideas of what may be going on? Im in the process right now of removing the fuel filter and the lines to put on new ones, and am also taking out the tank to clean it. Does the filler neck seperate from the tank or do I just have to pull it all out? Thanks