I bought a 1968 PA 28-235 this year . I’m still making friends with the aircraft. Learning a lot . One of the issues that baffles me is during cruise I seem to run out of forward ( nose down ) trim. The W&B is within acceptable limits. Above 130kts I seem to run out of forward trim. To hold a consistent altitude I need to slow the aircraft down . Is this normal or is the aircraft rigged improper? I typically run @ 65% power (22 square ).