Re-read the rules and they say you can only re-roll dice ONCE..

So as i understand this you cannot combine:

-Target lock + predator

or

-Han Solo + target lock

or

any other combination that allows you to re-roll dice during the same attack.

Is this understanding correct?

NOTE:

This post concerns the re-roll of dice during a single attack, not the use of gunner or luke skywalker which allows "new attacks"

Correct.
Each individual die may be modified any number of times in an attack, but only one of those modifications can be a re-roll.

That being said, TL + Pred, or either + Solo, do have their benefits. Predator allows a re-roll without needing to spend your TL, and both allow a selective re-roll which Solo does not.

I do NOT believe you have it right.

You may only reroll a given die once. If you have multiple re-roll abilities you CAN use all of them but just not on the same dice.

Example: Han is equipped with Predator and has a TL on an a target. When he attacks the following can happen.

1. Han uses his ability and rerolls all dice leaving no dice that can be rerolled.

2. Han uses Predator to reroll one or maybe two dice. He may then spend the TL to reroll any number of remaining dice or his ability to reroll all the remaining dice.

3. Han chooses to spend TL to reroll some number of dice. (NO, I don't know why he's doing that first.) If there are dice that have not been rerolled he could reroll one of them with Predator and then any remaining ones with his ability.

Now most of the time you will not want/need to use multiple rerolling modifications but it IS an option provided you to not reroll dice that have previously been rerolled.