Darkwa, 26, originally signed on with the Dolphins as an undrafted free agent out of Tulane back in 2014. He spent just a few months in Miami before he was signed off of their practice squad by the Giants.
New York brought Darkwa back on an exclusive rights contract in 2016 and re-signed him to a one-year contract last year.
In 2017, Darkwa appeared in 15 games for the Giants and rushed for 751 yards on 171 carries (4.4 YPC to go along with 19 receptions for 116 yards receiving and five total touchdowns.
Sims, 27, is a former third-round pick of the Buccaneers back in 2014. He played out the final year of his four-year, $3.104 million contract before returning to the Buccaneers on a one-year contract this past April.
The Buccaneers placed Sims on injured reserve last month before cutting him loose with an injury settlement a few weeks later.
In 2017, Sims appeared in all 16 games for the Buccaneers and rushed for 95 yards on 21 carries (5.9 YPC) to go along with 35 receptions for 249 yards receiving and one touchdown.