2008 GMC Sierra 5.3 failed lifter

[aaronq6]

I was in my truck (GMC Sierra 1500 5.3 liter) going down the highway when I heard a knocking that was gettting rapidly lowder. Talked to a couple different mechanics for them to get them steth on it and they all said the same thing. Time to replace the engine. I did get one opinion that it was just a failed lifter so I stripped the engine down to find out what the sound was before i went to replace the engine. I found that my number 1 cylinder lifter was collapsed. So I replaced the whole side with new lifters and put back together. I thought all my problems solved, the truck was running great for about 40 miles and I heard the similar knocking noise. So I proceeded to take the engine apart and the same new lifter had collapsed again. I have talked with several people to narrow down what the problem could be. Many people believed that one lifter wasnt getting oil to it, but I was told if that one lifter wasnt getting oil to it none of them would. So that assured me that an oil galley wasnt plugged. I have had some head work done to clean it up and to make sure the valve was functioning properly. They did a valve grind. I was thinking about going ahead and putting it back together but wanted to see if there is anything more I should take into consideration before i run into the same problem. Also i noticed that the new lifters that i I have are a bit longer (picture). Would this possibly be the problem with the new lifters or is this from simple wear?

 

Any insight on this topic would be greatly appreciated.