So I'm hoping the great diagnosticians of ls1tech can assist me. I have an abundance of evidence to form hypothesis on.....first some basic info

1997 Trans am
Automatic
5.7 lt1

The car has been missing. It is fine when I start and drive it. For about five miles it has lots of power and drives smooth, it runs down the road at 60 mph at a bit over 2k rpm

After a short while of steady 60mph driving the rpm drops to 1.5k and it feels like it shifts (likely the loss of power)......if you lightly press the gas it will sputter....but if you put it 1/2 to all the way down it takes off fine......also it drives fine in the city.....I can hold it at 1.5k at 30mph with no missing. (that I feel at least)

I had the codes ran
Multiple misfires
Egr valve (but I replaced it in march)
Thermostat ( I took it out for months but replaced it tonight)

I replaced the plugs and wires, no change


Trans rebuilt about 2000 miles ago

Some ideas I am pondering
Head gasket
Opti spark

Do you have any ideas?

Are there any ways to test the head gasket or the opti spark to know for sure?

Thank you so much!

 

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