67 twin turbo dart

You’re attachments aren’t working. Given the “brakes on” comment, I would be looking for issues with driveline, like transmission or converter. How does it shift? The feel of that would make one look closer or rule that out. It still doesn’t explain the cut out at exactly 4000 rpm. That looks suspect for engine issues. What do the plugs show? Those should be your go to for anything tune related. The widebands will lie to you, the plugs always tell the truth.
Fixed. Yeah they checked the trans and found the bands loose, and found that the carriage bolt holding the kickdown block off had dropped its nut into the pan and the spring pressure plate was missing a bolt . They say it moves better not like it was, that's why I'm wondering if the clutches are bad, since the bands were loose and not fully engaging, course I only drove it that once down the street and back. I wrote PTC to see what the stall is on that converter, here is the description 9.5 TF-8 15-0x45 .090 SL. Plugs were black and they changed then out to some NGK copper ones, had NGK iridium's in it.