Keep in mind that your Jetta probably has a slightly different injection system - I think the Fox's CIS-E system is unique though similar to MkII CIS.
One thing to check - there is a screen in the fuel lines at the fuel distributor, it's there to catch larger chunks left in the gas tank from assembly. I forget exactly where it is, and don't know for sure that your Jetta has one, but given what you said about gunky fuel I bet if you have one it's pretty nasty.
Definitely clean your injectors. Might wanna pull the tank and have a pro clean and coat it.
Check the rest of your fuel lines - you might have a crack somewhere that's leaking pressure.
Keep us posted~!