I don't believe there was a difference in uniforms between Grenadiers and panzer grenadiers. They're just mobile Heer infantry.
SS panzer grenadiers had specific camo but the grenadiers wore what they could get (especially late war). In North Africa Grenadiers wore American, British, and Italian uniforms...anything they could salvage/scavenge.
To break it up and specify panzer grenadiers you may wanna try to pick out models with the baggy smocks and give them camo to make them seem more 'elite' then foot sloggers.
Its tough at first to shift from 28mm to 15
mm. You dont need as much detail...maybe a dark base color, the final color, wash it and do highlights in the final color again. Then when done drybrush everything with a grey or bone color.
gl