I did a compression test on my 95 4.9L today. I don't really know a ton about the optimal ratios, but my results came back 1-150, 2-150, 3-120, 4-125, 5-120, 6-150. I'm guessing it may have a blown head gasket between 3-5 cylinders?

 

Those compression readings tell me the engine is in good mechanical condition, there is no way possible you could have a blown head gasket just between cyl 3&5 without #4 in the mix. Straight 6 engine cylinders number 1-6 front to back.

Rather than trying to self diagnose and throw yourself into a $$ pit, why not describe the issues that concern you, then some of the experienced people on this forum can point you in the right direction.
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The idle is rough despite fresh oil, filters, and full tune-up. It's not just that it's rough that bothers me but the way it runs. It seems to surge slightly every 1-2 seconds and then run smoothly after. The surge shakes seat and steering wheel slightly but enough to feel. It's very odd. I've tested the IAC and tried to look for vacuum leaks to no avail. The engine surges religiously about every 1-2 seconds at idle in park. It may surge in gear as well but I haven't noticed it. Cleaned throttle body today, didn't seem to help

 

Have access to a scan tool? Really need to look at sensor readings in real time for an accurate diagnosis.

If the plugs are in good shape those symptoms could be caused by a myriad of items and in my experience over the years sounds like a classic case of a bad O2 sensor but I wouldn't condemn anything without looking at live data.
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