cant help you much,, I had your same set up in my 52 halfton,,,patricks 3:55, their modified sagnaw four speed shifter.......drove it a lot on the free way,, no problem except the high rpm even in fourth it would be close to 3000 at 65.........
the enclosed petered out so I just went ahead and had a s-10 five speed and blazer 2:73 rear ... I can now got 65 at about 1800 rpm.......a lot less strain on the engine.. I like it real well.. I drove the patricks set up for about 5 yrs,,not bad but I like my new set up better, like to drive it on the hiway.......not much help to you but I do under stand your problem.
