More details would really help, or maybe more test driving on your part.
What truck do you have exactly Year/make/model/engine/transtype/other mods you've made?
When it was slow getting up to speed did your turbo spool up properly? Did it get down into low gear or did you try manually shifting into low if it's an auto? Did it go into limp mode (if automatic)? Did it sound any different driving otherwise? Do you have extra gauges with your chip for EGT/boost or anything else that might tell us what state things were in? When you say it revved, but was slow, do you mean you just couldn't accelerate as quickly as you expected with the 120 setting, but was it otherwise normal for stock/standard? Did you try other settings on your chip and get the same results? Could be your chip is acting up, could be it went into limp mode if it's automatic, could be your turbo isn't spooling up, could be you popped a leak in the pipes for the turbo. could be a lot of things, but details will help narrow it down.