VW GTI 1988 Fuel Problems

Hello ALL,
I have been having problems with my 88 GTI Fuel system. The engin is a 2.0 L with a 1.8 L head, that has been polished and ported. The engin ran great, until I changed my IN-Tank Fuel pump. I changed the pump when I noticed the car running out of gas when the guage reached a little below half a tank. I purchased a new pump and completed the instal. When completing these repairs I installed a new distributor (Same part number as before) and the car started to idel terribly when cold and when warm was not much better. (I switched Distributer back to ensure no error on parts, but problem was still there) I checked the timing and everything is on and this was verified by NewGerman Performance (NGP) a local shop. I decided that possibly the fuel filter has been clogged, when I installed this new pump. I changed the Fuel filter and the car seemed to run slightly better, but still has these idle/performance issues. The car would start, but would struggle to stay running for 5 minutes and then would somewhat stabalize, but when I go to drive the car, it is hard to keep running when coming to a stop and a major loss in power.

Actions I have taken:
New In-tank Fuel Pump
New Fuel Filter
Pulled apart Fuel Distributer to ensure no blockage
Check spark-plugs and installed NEW
Fuel Air Mixture was set by NGP and verfified by others
Checked Cold Start and seems to be fully operational

Possible options?:
Thoguht of getting a fuel enrichment mod, but don't want to spend that cash if that has nothing to do with it. I'm trying to sell the car and I want to make sure it is running well.

Anything you all can suggest would be very helpful to me!

Thanks!

Does this engine still use a knock sensor, it can cause similar problems as it modifies the ignition timing signal? Also, as the base ignition timing & set mechanically and the ECM does all the fine tuning I'm wondering how the timing was checked. If you only used a timing light it may be misleading as the ECM can be adjusting things to look okay at idle when it may not be. I'd go back & set the engine on TDC & check the distributor rotor alignment to the notch on the housing (mechanical timing). What I'm thinking is that the distributor may be off just a tooth and the ECM is correcting enough for idling. But, when you try to drive things go really bad and the ECM can't adjust.