If your house is only 4 years old, and your system has already failed due to poor soil, replacing the field probably won’t help much. If it were twenty years old, and the gravel in the field was clogged (not likely in 4 years), but the soil was good (yours is not), it might help.
Before investing in a new field, get the soil retested and run a new perc with someone you trust. There are a number of reasons that the original tests could have been bad, including incompetence, or even kickbacks from developers to get permits in areas that should not pass.
Depending on how bad your tests are, you MAY be able to increase the size of your field to compensate for slow drainage. Unfortunatlely, you may have to double it to have a noticable effect, and to be certain you will cure the problem.
Don’t rush into this without retesting–the tests are cheap compared to replacing the field. You don’t need another failed system. Good luck.