I have a hard time shifting into 1st and 2nd gear

Sounds like you need a clutch. What happens is when the clutch and fluid heat up they stop operating properly and the clutch doesn't completely disengage which makes it had to shift.

Here are a lot of guides on this:

https://www.2carpros.com/articles/clutch-symptoms

https://www.2carpros.com/articles/clutch-doesnt-work-sometimes-or-not-at-all

https://www.2carpros.com/articles/how-to-replace-a-clutch

https://www.2carpros.com/articles/throw-out-bearing-replacement

https://www.2carpros.com/articles/pilot-bearing-replacement

Plus below is the process on how to replace the disc from the manual.

I would replace the entire system including the slave cylinder, pressure plate, and disc.

Please let us know if you have other questions about this and we can go from there.

Thanks