F150 auto trans slipping 1st & 2nd. No check engine light. Help plz

Im aware how expensive it is to install new, would you put rebuilt or used one in yur vehicle?

When was last time some new fluid was replaced in transmission? How is the fluid level? Regular service intervals of drop and refill during the life of this transmission? Your choice on rebuild or new. How Long do you plan to keep vehicle and how Many miles on engine and chassis? 200K+? Buy different vehicle if so.

Nothing much a consumer can do with tranny problems other than checking the fluid level. New trucks are expensive. And the problem with a used truck is one does not know what the previous owner did about periodic maintenance. It appears you will need a rebuild at the least, but have a professional check the tranny first. Now for cost. No way would I install a used tranny. You simply don't know what your are getting. Rebuilds require labor costs of removing and reinstalling the transmission after the rebuild. Now compare the cost of rebuilding the transmission as compared to purchasing a re-manufactured one. Ford re-manufactured trannys come with something like a 100,000 mile warranty with five years of so warranty. Look at the dollars and see what is best for you.