Tell me that you have reverse gear when the transmission is cold - the same clutch is used for reverse and High gear. If you have reverse but no high gear then it is the valve body (probably the kit that was installed) or a linkage adjustment problem. The dipstick popping out could be a result of the problem but I would look at the vent first. Make sure it is not plugged or stuck closed with paint. The top of the vent should wobble freely.
Check the fluid level with the engine idling in Park.
Let me know what you find.

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Paul
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retired mechanic after 35 years
specialized in Holley carbs and Ford Automatic Transmissions