If you have been issued both slips, you need to report them both. There is different information on the slips, although it would appear they relate to the same investment.
The T5013 slip shows investment income and expenses within your Limited Partnership. (or activity in account).
The T5008 or December 31st account statement shows capital gains or investment income based on YOUR buys and sells. (usually only received when you sell or cash out).
If you feel you have been issued one of these slips in error, you should contact your investment advisor and verify this. If a slip has been issued in error, you will need to have it amended, especially as CRA already has both slips in their system.