Diploma

1. M.Tech : If you want to go for GATE exam then you have to have the basic understandings of your core B.Tech subjects like c, dbms, automata, computer architecture etc. Though it is not impossible to have a fresh start but it will take time and money also so if you have knowledge of basics about all CSE subjects then you can go for GATE. Just drop a year and take a course of Ravindra Ravula and be dedicated and study hard ! You will surely crack it. IIT tags can take you to a completely different level in professional life. Mind it!
2. MBA : I will not suggest you to go for MBA immediately after B.Tech because even if you score 99.2percentile or more in CAT then also it will be difficult to get a very good college but if you have an experience of 1 or 2 years in IT and having the same score then it will be much easier for you. FYI, MBA will be much more effective if you have some experiences how any company works. If you don't want to go for further education then you can get a job in any IT company easily. But if you are not from IITs or good NITs then probably after 2 or 3 years you will feel that master degrees are helpful if you want to grow in IT sector. So better to have at least one master degree.