[Accelo]

Not likely the TV cable adjustment will help.
Very likely they installed either the Corvette Servo or a Billet Servo and/or bypassed the accumulator. Easy enough to change out the Servo, as it doesn't require pulling the pan.
If you have the Corvette Servo go to the stock one and if it's a Billet go to the Corvette Servo. Pictures of each style are available on the internet.

What many people don't understand is shift quality is very much affected by the differential gear ratio, the weight of the car and the stall of the torque converter. This is all taken into account by the OEM's. Once you change things their is not much control over shift quality/firmness.

If you are not comfortable with this work most local shops will change this out for you. It's a 30 min job, maybe less? Consider if you mess with it any warranty you had will typically be null.
Cheers