Leaving the EGR disconnected could cause pinging that could damage the engine, and the service engine soon light will eventually come on, if the EGR is not working.
If disconnecting and plugging the EGR helped, the first step is to identify which type of EGR valve/system your truck has.
Positive back pressure EGR valves - Should have a “P” after the last numbers on the valve. The pressure in the exhaust system effects (modulates) how much the valve opens.
Negative pressure EGR valves - Should have an “N” after the last numbers on the valve. The pressure in the exhaust system effects (modulates) how much the valve opens.
Port EGR Valves – The EGR solenoid pulses like a mixture control solenoid/fuel injector to control vacuum supply. Port valves have no “P” or “N” and it is blank after the last numbers on the valve.
TBI trucks are generally Negative pressure EGR or Port EGR systems.
This is a site that has a photo and an illustration about EGR vale numbers
http://shbox.com/1/EGR_ID.jpg
EGR valves have a spring in them that can get weak causing the valve to open to much or to easily.
Exhaust system backpressure can greatly effect the operation of the EGR valves on many vehicles. Modifying the exhaust system can effect how well the EGR works if it changes the pressure in the exhaust system. Exhaust back pressure (from a restricted converter) or no back pressure (from no converter or mufflers) can have an effect on how much the EGR opens.
Have you modified the exhaust system recently?
If you find it does need an EGR valve, I would suggest only using a general motors replacement EGR valve. Double check to make sure they sell you the correct EGR valve.
Note: A lean condition caused by another problem can be magnified when the EGR valve opens.