Hi anish,
Congratulation for your rank .
Best nits you can get for cse or mechanical.
But with obc rank 5000 you cannot get computer science in any well reputed nits but still if you want to know.
Then for mechanical engineering.
Nit surat,
Nit patna.
Nit nagpur you can give a try in special round.
Nit jamshedpur., Nit kurukshetra , nit bhopal.

And for computer science northeast nits like nit sikkim ,nit aizwal , nit shillong .

So better for you is to take admission into reputed nits with mechanical as branch than in worst nits with computer science as branch.

Hope it helps !!!