Unique doesn't generate enough pressure in the 38 to burn clean. Try Titegroup.
Agreed. .38 Special and .357 Magnum are two very different pressure bands. Just because the reloading manuals list data for a given powder in .38, .45, and .44 Magnum, doesn't mean the powder will be very happy to operate in all those cartridges.
For .38 Special, Bullseye and Winchester SuperTarget have served me well. Lots of people say nice things about Titegroup and HP-38/WW-231 (I wish I could get some locally, but no dice). Both the BE and WST meter beautifully even at tiny charge weights, and burn clean.
For .357 Magnum, Universal has burned adequately at those pressures, but I haven't been super-satisfied with it. There's always more smoke, more unburned powder and residue, and larger groups than Unique, no matter how how or cold the load. I know a few 9mm guys that have been very happy with Hodgdon CFE Pistol, at more or less .357 Magnum pressures.
Oh, and when looking for a replacement powder, I'd also suggest swapping primer brands if that's acceptable to you. It can make a big difference.