[HELP] Daewoo Solar55-V, Boom up is very slow while pulling both arm and boom together

Hello Dear!! From South Korea, I bought an old excavator(2003), and here is my situation. #1, Boom up is too slow compared to arm when I pull the both levers together(arm, boom). #2, When I release the arm lever while pulling both levers, then Boom is moving faster. #3, When I pull the arm lever while pulling boom -> boom gets very slow. #4, Boom up is very slow while both tracks are moving forward or backward.(arm and boom down is fine) #5, Single operation of boom up itself is quite slow #6, Boom down is fine regardless of single action or simultaneous actions. I've spent 1,000 dollars on it already but she wanna more Holly.... Guys please give me any tips. Thanks a lot!!