Joined the 5.0 crowd today

[69fastback]

well I finally did it I now have a 91 GT. It is a very good looking car it is balck with grey leather interior. I couldn't believe how nice the car is I had to get it. It looks like it did back in 91. There are some mods done to it. I can tell it has gears I think they are 355s the spedo says 10 mph to fast. It has traction bars and a full exhust headers off road h-pipe and flowmasters. Plus it has a msd 6a. The trans is an aod with some work done to it I can tell it has a shift kit but i don't know if it has a higher stall converter or not. The guy was telling me the heads or not reguar 5.0 heads that they have a spark plug like the gt 40 heads do but there are no markings on the heads. Can someone please tell me what to look for to find out what kind they are? The only thing with the car is it does not like low rpms it doesn't idle very well it has an eratic idle then if you are just crusin along it kinda surges and sputers but when you hit the gas it takes off like a rocket. It takes of really well and is smooth as hell just doesn't like to cruise around with gas pedal in the same place can someone help me with this? I fiqure it just needs an adjustment somewhere????? I will post pics when i get a digital camera. It has only 64.000 miles and i got it for only 4,300 i thought that was a great price.