Won't go into first when warm/Reverse Grind when warm

The car does not lurch forward in gear and clutch pedal depressed. The car was great for the first 1000 miles and nlw thos problem rears its ugly head. It goes into the other gears fine and is not a problem when rolling. So weird because as you are driving and shifting, you would never know anything was wrong. If the bellhousing was mis aligned would it have shown up rigjt away and not 1000 or so miles later? I have tbe tranny out and forl. The fork looks om but do they have a tendancy to bens and crack? I also bought new gear fluid. I used Jaime Passons fluid, but thought I should switch to a different type to rule that out. The centerfoecea pressure plate shows some signs of heat in a few spots, but not crazy. Disc visually looks OK. Just frustrating. I tried to do the magnetic base dial measurement foe runout, butwas not sure hpw to exactly get the two arms to work and get the dial in the right spot. I got frustrated and left the garage. Thia big block dour speed swap has been such a learning process. About to gove up after having this car for 26 yrs.