[fiveohpatrol]

your heads are certainly the bottleneck of it all, but even so you should be getting a ton more mph than that. Hell, with GT40P heads on my 347 (huge bottleneck) I trapped 112mph. You've got better flowing heads, and 46 more cid!

Are you aware of where the timing is? Even if it is off a few degree's of where it "likes it" you will lose a lot of power. Have you read your plugs after a run to check how its running?

Another thing to consider is your torque converter. I helped build a car with a C4 recently, and the thing made a ton of torque down low, but just wouldn't pull up high. Well, we put it on a dyno and noticed that it made a peak of 350ft-lbs of torque at only 2800rpm (and was still climbing hard, ie, steep graph) but then the converter was crapping out and not allowing it to push any more power through.

Just another possibility.