if the afr's did not change with the new fuel pump then you do not need to retune. But the fuel system is not your problem. if you are really worried about the number and don't want to spend a heap of money, get a dyno run from another shop and see how it compares, some shops strap cars down way too tight which can rob power, but if they do this for the before and after you can still see the legit gains. There are tests that can be done to work out if there is an issue, but that's not normally included in the cost of tuning, talk to Gentech about whether they did any test or just tuned it and whether they are prepared to diagnose it for you. Without trying to be smart so forgive me if it comes across this way, but you did the combination, you purchased the parts, you may have to accept that there is an issue with a part you have supplied. If you purchased a package from the tuner and they guaranteed "X" amount of power with the combo and it did not make it, it would be up to them to find out why, whether an issue with a part they supplied in which case they would chase up the supplier, or whether there was a problem with the car which would fall back to you. Tyre types can affect dyno readings as can wheel size, I know for a fact that Nittos rob power and are inconsistent on the dyno, great on street, not great for tuning. I had a G6ET once that would not go over 280 rwkw even though it had a 100 cpi high flow cat, a change to a 200 cpi cat and it went 305. The small turbo will not hold high boost in the top end and choice of hardware will impact how much boost it will have, some tuners have spiked the midrange up to 18 psi plus hoping to carry a little more boost in the top end, not really ideal for a nice driving car. Gentech are good at what they do, talk to them and see if you can work out a plan of attack if you are concerned