My character has 19 Dex. Gave him Gauntlets of Dexterity +1. In the character sheet, his Dex is now at 20, but his Dex bonus is still just +4. Anyone know what can be causing this?

It's likely you armor. Take it off temporarily to see.

The character sheet shows the Dex Bonus as it applies to AC, so you only get as much as applies to your current Armor.

Though AFAIK, you still get full bonus for most other things. Like attack bonus if you are using bows/weapon finesse.

Yup! Forgot I was wearing Studded Leather, thanks! Though it seems that wearing it also prevented the +1 from applying to other bonuses, which seems weird.

This is incorrect. You'll suffer the Armor Check Penalty but you still get your full Dex bonus to things like Hide/Move Silently. Try making a new character, give them full plate, then set their Dex to 100. You'll note they have 30+ Stealth now from that insane Dex score.

I meant ACP for the skill penalty, MM (he stated he was wearing studded armor which will reduce most DEX skills, like the stealth ones, by 1). The MDB only limits the DEX AC. When it (the MDB) is less than the ability's potential, the modifier displays in red. Neither limitation affects Reflex.