It doesn't go above 40 even when i step on the gas it only stops at 40. I changed the catalytic converter it still does not go above 40.
You need to scan your vehicle before you decide on any action plan. With a scan faults on the engine causing limp home, faults on the trans causing slip or not changing gear will be indicated and can be investigated. It looks like you have spent $200 or $300 hundred dollars on a quess, unless something else, damage?, was wrong with the cat.