I do not think your issue is Replication. I think it is either I/O or bad indexes (or both).

A few things to look at on your side:

How wide is your table (how many columns and what is the predominant datatype)?

How long is your table?

How many indexes does your table have? You might have too few. You might have too many. If the total # of indexes is half or more of the total # of columns, you have too many. If you have 0 indexes, you definitely have too few.

Is your paging file the proper size? Does your hard drive(s) / SAN(s) have the proper amount of free space for reading and writing on both sides of the Replication connection?

Network problems are a possibility, but I would concentrate on indexes and I/O issues first.

EDIT: Get your server admin involved for the I/O issues questions.