My car will not accelerate after 30-40mph. Can someone help me ?

No there is no check engine light on. The rpm keep going up and down

When cold if you can lightly hit the converters with a rubber mallet/hammer of the side of your fist and hear rattling you may have broken pieces inside restricting acting like a wet vacuum when full and check ball stops air flow but normally would have a DTC like a P0420 for CAT Efficiency. If fuel filter is dirty and limiting fuel flow or fuel pump capacity down that too can cause and limit speed but would often have a lean DTC, if air filter is real dirty and restricting air flow can cause problem too but there again would often get a DTC that would turn on check engine light. When you turn key on just before the cranking position all your warning light s should come on KOEO lamp test (key on engine off), does the check engine light come on then, it should, if it does not you may have codes and do not know it because of light not working. What is the VIN number?