1997 K1500 Silverado trouble
 

Hi, I have a 1997 K1500 series 4wd 3 door 5.7liter,silverado truck
I had it to the shop to see what was causing a rough,studdering, ride ,it doesnt happen all the time,but when it does I notice it when I get to 30-45mph,it acts like it wont stay running,i have to give it gas and it does stop after i exceed 50mph and its a nice smooth ride. I have had many parts replaced,sensors,tune up fuel injectors cleaned,new fuel filter,cleaned the intake,I cant remember all the sensors that have been replaced,but so far it still has the same problem it had before I took it into a shop and they charged me quite a bit of $$ and it still isnt running right. I really need to find out what it is and any and all help/suggestions would be great! I was told that maybe it is a bad air line or something to do with the air flow is either too much or not enough? Thanks!

I also needed to know about the timing for it. I am not too familiar with mechanical issues,so again any and all help would be great!