Ok couple years ago replaced the lower intake gaskets evry since then tahoe has stuttered under a load ( going up hill ,etc) mostly at hiway sppeds more noticable. I did not have a code reader at the time so, rmoved lower gasket 2nd an 3rd time , quad. check distributor , wires etc. and I still have a miss , starts fine drives fine. Set a SES light when I drive it and this is the codes i found. first was P0305, second is a P0300, P0463 which is why the fuel guage is bouncing alover I am sure. Also the plugs seem to have some reddish brown on them? mostly on the ceramic part and only on onside the it is more noticable. I am thinking a injector , but the spyder was replaced an still the same stutter. any Ideas be great. coolant pressure has dropped 1/2 psi in a hour or so. the compression is
cyl 1- 120 psi cyl. 2 - 150 psi
3- 120 psi 4- 150 psi
5- 150 psi 6- 150 psi
7- 120 psi 8- 155 psi

The freeze frame for the P0300 says:
Fuelstatus bank one: closed loop
Fuel status Bank two: closed loop
calculated load : 46 %
coolant temp : 198 *
long term fuel trim bank 1 : 2.34 %
short term fuel trim bank 2 : 1.56%
long termfuel trim bank 2 : 2.34
intake manifold absolut press. : 28.6 in.HG
eng rpm : 2264
airflow frome mass airflow sensor : 13.74 lb/min
absolute tps : 67%

 

use this plug readerNGK Spark Plugs USA

 

kinda looks like the Insulator Glazing one but more red color. doing a radiator/ coolant pressure check now have lost about 1 psi in like 3 hours now . I wouldn't consider that bad really.

 

Should I have vacuum at the oil filler when I cap off the valve cover breathers? getting about 7 psi of vaccum through the oil filler tube. or is this a upper intake leak?

 

Will loose that much pressure in 3 hour from cooling of engine.
Should not have hardly any pressure at oil tube.
Start checking for vacuum leaks.