Can a student with an 8/7/8 academic record be selected at IIM Ahmedabad? Is getting into IIM Ahmadabad that difficult?

Depends on which category you belong to, with the above-mentioned grades if you are from the general/open category then you will need a really good CAT score and percentile to get a call from IIM-A, which is anything above 99 percentiles, even with that it is not certain though (because it depends on some other factors as well). And all this only to get a call from there, the story does not end there, you have to do really well in the GD and PI sections. So, yes, getting into IIM-A is difficult but that does not mean it is impossible.

The best advice for you right now is to focus on scoring well in CAT and please do not fixate yourself on only IIM-A because IIM-B and FMS (except the tag) are at par with IIM-A.