We have a new gas dryer, new vent and vents outside. Vent is about 8" long and straight.
Our towels after being used once smell kind of sludgy. We replaced our copper lines with ABS, replaced our washing machine with new front loader, thinking this was the problem. I noticed when we replaced our copper pipe (rotted) the smell was the same as the smell we get from our towels after showering, our dish cloth smells the same after first time being wet. Our clothes are fine, only towels seem to have that smell. I noticed a while ago the dish cloth smelled when sitting on the sink. Could this be a plumbing issue?
It's a terrible smell, and coming out of the shower to dry off with a "clean" towel that smells.
Any suggestions?

You will have to clean the drier out thoroughly. Every air duct will have to be removed and scraped and washed out to remove baked on lint deposits which is like concrete lining. This will burn so the manufacturer has installed the safeties to keep from having a house fire. Driers were the number one cause of fires at one time. Look at: http://www.youtube.com/watch?v=MMP7BW1lLs4 to see how. Also: http://www.youtube.com/watch?v=iBiRw-KElC4 ; http://www.youtube.com/watch?v=yFTZGgVisCI
When you finish cleaning the drier it is best to also replace the belt, too, because you do not want to have to disassemble it again, and if the belt is over two years old you should replace it.

Note that on most of the videos it does not show them washing out the parts, but this is important because it's the only way to really get the parts clean, just don't get motor wet or the capacitor if it has one. Vacuum out motor. I would move the drier out to your garage to have plenty of space to work. You also want to check your vent and clean it, also. The job is really easier than it sounds. There is no shortcut that will work; it has to be cleaned well. Before you re-assemble it make sure to use white lithium grease (high-temp grease) and grease all bearings. Just vacuuming out the dryer a little does little good. You also want to check the vent and clean it out. When you are done you will have a new dryer and it will dry like new again. You want to clean it like this every two years or every year with many children. DrTom4444

Thank you for your answer. But the dryer is brand new as well as the vents. Other answers were given suggesting the P trap. When we took the plug out, we found the smell to be similar to what we were smelling on the towels

What are you talking about when you say P-trap? There is no P-trap on a dryer. P-traps are in drain lines to prevent sewer gas from getting into the house. If the dryer is new you have something in it that's not supposed to be there. Maybe it's something in the gas line. DrTom4444