No, Slaking is not a pseudo legandary. First off, the requirements for a Pokemon to be considered a pseudo legendary are:
- A base stat total of exactly 600, no more, no less.
- 1,250,000 experience points at level 100, known as a "slow" growth rate.
- The Pokemon must be the third in an evolutionary line of three.
Slaking has the second and third, but not the first, because it's BST is 670, not 600. Slaking goes even further downhill with its ability, Truant, which kills any remaining chance of it being a pseudo legendary.
The thing about having two of the same Pokemon on one team is wrong. That isn't a requirement.