Please help..I have a 98 Silverado with a 5.7 Jasper engine w/20?k miles on engine and 110K miles on truck. As of late it developes sluggish engine issues over 40 mph and when warm it starts like it has hot timing. There has been a SEL on for sometime. I believe it has to do with the cat converter. However problem only seems to appear during wet conditions.Any help would be appreciated.

 

Check distributor for moisture. Could be converter stopping up.
Check front of converter how warm then feel after converter .. should be same temp.
If pipe in front gets hotter than after .. probably stopped up.

 

I would look for something breaking down in the ign. If you want to check conv. remove o2 sensor and check press. Shouldnt be over 3 lbs. approx.

 

What might be some of the things in the ignition to look for?

 

whatever happened to checking the codes 1st?

 

You never heard "when all else fails read the directions" same here,and if you insist on this weird behavior we may have to recend your "mans union card"

 

I m just saying, you know, if the car was built with OBD II for this specific purpose why should we guess?

 

Of course you are correct. Back in my day they didnt have these things so I forget to mention this. Much the same reason that I got pulled over for not using my turn lights.