...um, Trunks never went SSJ3. The only SSJ3s in the entire DB/Z/GT compilation were Goku and Gotenks. In terms of SSJ transformations, here is how it goes:
Goku: GSSJ, SSJ, SSJg2, SSJg3/USSJ, FSSJ, SSJ2, SSJ3, SSJ4
Gohan: SSJ, FSSJ, SSJ2
Goten: SSJ
Vegeta: SSJ, SSJg2, SSJg3/USSJ, SSJ2, SSJ4
Trunks (Chibi): SSJ
Trunks (Future): SSJ, SSJg2, SSJg3/USSJ
Gogeta: SSJ (possibly SSJ2 and SSJ3, but SSJ was the only one shown), SSJ4
Vegito: SSJ
That's basically all the Saiyan transformations shown. Legend:
GSSJ - Giji Super Saiya-jin/False Super Saiya-jin
SSJ- Super Saiya-jin
SSJg2 - Super Saiya-jin Second Grade
SSJg3/USSJ - Super Saiya-jin Third Grade/Ultra Super Saiya-jin
FSSJ - Super Saiya-jin Full Power*
SSJ2 - Super Saiya-jin 2
SSJ3 - Super Saiya-jin 3
SSJ4 - Super Saiya-jin 4
* - In this form, there is no energy depreciation, and the unwanted personality changes are not present.
Goku: GSSJ, SSJ, SSJg2, SSJg3/USSJ, FSSJ, SSJ2, SSJ3, SSJ4
Gohan: SSJ, FSSJ, SSJ2
Goten: SSJ
Vegeta: SSJ, SSJg2, SSJg3/USSJ, SSJ2, SSJ4
Trunks (Chibi): SSJ
Trunks (Future): SSJ, SSJg2, SSJg3/USSJ
Gogeta: SSJ (possibly SSJ2 and SSJ3, but SSJ was the only one shown), SSJ4
Vegito: SSJ
That's basically all the Saiyan transformations shown. Legend:
GSSJ - Giji Super Saiya-jin/False Super Saiya-jin
SSJ- Super Saiya-jin
SSJg2 - Super Saiya-jin Second Grade
SSJg3/USSJ - Super Saiya-jin Third Grade/Ultra Super Saiya-jin
FSSJ - Super Saiya-jin Full Power*
SSJ2 - Super Saiya-jin 2
SSJ3 - Super Saiya-jin 3
SSJ4 - Super Saiya-jin 4
* - In this form, there is no energy depreciation, and the unwanted personality changes are not present.