Most of the 1 ton trucks have a Port EGR valve in which 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 Origional factory valve.
The testing is much different then a ½ ton negative backpressure system.
If you verify it does have a Port EGR system, then the EGR valve you buy is not so critical because it is a simple diaphragm.
Negative backpressure valves have more going on inside then people realize.
The TBI trucks with this valve are very picky about its operation and you want to stay with what is came from the factory with.
Here is a site with a good illustration of a negative back-pressure EGR valve.
http://shbox.com/1/EGR_valve.jpg
The easiest way to identify a Port system is by the EGR solenoid. This thread has a photo of a Port EGR solenoid.
http://67-72chevytrucks.com/vboard/s...48#post4083748
I kept this as short as possible not to highjack his thread and make it to long, but I thought he may be wondering the same thing.
Truckfan you can send me a private message with a link to a thread of yours and I will talk more there.
Posting photos really helps me, help you.