So your that far into it There is a cleaner kit I bought on E-Bay it consists of two plastic tubes and two power assemblies. The plastic is to put the injector in and set it on a pressure spray can of injector cleaner, Next use a 9 volt battery to open the injector valve don't hold the battery connected for long period just touch the clamp on and off rapidly the battery terminals until the injector sprays a fine mist. HANG on to the injector as the pressure will blow the injector across the shop. The cleaner kit is cheap (less than $25.00) and can be used on many other of different manufactor's injectors thus the two different electric connectors and plastic injector holders.
This worked fine for my misfire. Be SURE to clean your top side thoroughly so dirt doesn't get in engine during tear down.
This kit is far from fancy and it is inexpensive. all you have to by extra is a spray can of injector/MAP cleaner take the spray top off the can and set the injector holder on the top of the can push down to inject the cleaner.

 

Good to know. Thank you!

 

Sorry I did it again........... your talking about a 4.8 V6 the engine I have in my 99 is a 5.3 V8 different situation My 4.8 in my Astro I just replaced the spider assembly which is updated assembly.
The astro injectors are a real pain to clean. The way I did my Silverado was easy and didn't have to take anything off except fuel rail with injectors hanging off.

 

Mines a 4.8 V8. Same as your 5.3. They're attached to the fuel rail. I just ordered the spray cleaners from Amazon. Only $15. I have Prime so it'll be here Friday. My knock sensors and harness would t be here until Friday anyways so I'm hoping to get this all done Saturday.

 

I'm happy you got ME figured out LOL. I got confused my Astro is a 4.3 v6 not 4.8 seems to be happening more often lately.
Getten old I guess. It is an excuse tho.

 

If your 4.8 is about the same as my 5.3 check your oil pressure regularly as GM "O" ring on the end of the pick up tube will stop oil pick up. a simple fix if you take oil pan off but if you have to replace the pump the timing cover will have to be removed. I tried lassoing the bolt with fishing line so it didn't fall into the pan: it didn't work as I thought it would it fell anyway so a few cuss words and couple more hours I retrieved the bolt and reinstalled the NEW "O" ring.

 

My oil pressure seems good. My rear main seal is leaking a little bit. Replacing it myself isn't something I'm comfortable with.