With B now offerred momentum on interceptions and fumbles recovered inside the 5 yard line, I have a question. Does this apply to grounded fumbles...

scenario..

Its a rainy day and the field is wet. A fumbles at their B's 6 yard line and the ball is laying on B's 4 when B slides on the wet grass, secures posession at the 3 and then continues sliding into the endzone. B's ball 1-10 at B3?

You actually answered the question. A "recovered" fumble is always a grounded fumble. A fumble that is caught in the air is a catch for an interception.
When the word recovered is used it always means grounded. Fumble, kick, backwards pass, all the same.
When the ball has not been grounded the word "catch" is used. Note: you cannot catch a grounded ball.

So, can you recover a forward pass?

When you say he is sliding, do you mean on his belly or back? If so, the ball is dead as soon as he secures possesion.

Yes.

But momentum only applies if he was sliding while only touching the ground with only his feet and/or hands. Otherwise if he was sliding on the gound the ball would be dead at the 3 anyway.

As Dizzy would say - He wuz done down at the three before he slud into the end zone. Your play is not an example of momentum.

If B had secured possession at the three and stumbled into the end zone and downed there, now momentum is in effect and would be B's ball at the three.

Ah good point on my flawed description. But thank you for answering my question anyway... that clears that up.