Does the transmission shift ok if you drive the car easy?
I had this situation years ago. I only had the problem when things got torqued up. Look for clearance issues for the shifter and linkage rods. Also check all mounts and torque straps that have been added. You can't have any movement at all in the drivetrain for that 1-2 shift for some reason. Once I had good clearance and potential drivetrain movement in check, all was well.
Too many cars, too many parts, too little coin, too little space to work in, too little time left to make it all happen!
Update: down to one ride, still too many parts, a little more jingle in the pocket, gaining space, and it's going to happen this year!
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