quarter. The sales performance is a direct result of improvements in manufacturing throughput, as well as continued favorable demand trends in both domestic and international markets, partially offset by the strong fourth quarter results reported last year.
Rental Equipment Segment revenue was $7.9 million in the fourth quarter 2023, an increase of 7.3% versus the prior year, supported by strong end-market demand in key North Texas markets, including contribution from the Lubbock, Texas location that opened in March 2023. The Rabern business benefitted from the deployment of new rental fleet acquired in 2022, pricing gains, and our expansion into the Lubbock market.
Total gross profit was $16.4 million in the fourth quarter, an increase from $15.2 million in the prior-year period due to increased manufacturing throughput, improved pricing realization, and sales mix. As a result of these factors, gross profit margin increased 162 basis points to 20.9% during the fourth quarter 2023. Higher US-based steel prices were once again a headwind to gross profits during the fourth quarter, as steel prices surged late in the third quarter and into the fourth quarter. The Company continues to implement price increases and commodity surcharges to offset rising steel prices and expects to see some relief in the coming quarters.
SG&A expense was $10.8 million for the fourth quarter, compared to $10.1 million for the comparable period last year. R&D costs of $0.9 million were flat from last year.
Operating income was $4.8 million for the fourth quarter 2023, compared to $4.2 million for the same period last year. Fourth quarter operating margin was 6.1%, an improvement from 5.3% in the prior year period. The year-over-year improvement in operating income was driven by the solid gross margin performance combined with disciplined cost control.
The Company delivered GAAP Net Income of $5.2 million, or $0.26 per diluted share, for the fourth quarter 2023, compared to net income of $0.5 million, or $0.02 per diluted share, for the same period last year. The increase is driven mainly from a tax benefit recorded in the fourth quarter of 2023.
Adjusted EBITDA was $8.0 million for the fourth quarter 2023, or 10.2% of sales, consistent with the $8.1 million, or 10.3% of sales, for the same period last year. See Non-GAAP reconciliations in the appendix of this release.
As of December 31, 2023, total backlog was $170.3 million, down from $196.9 million at the end of the third quarter 2023.
BALANCE SHEET AND LIQUIDITY
As of December 31, 2023, total debt was $94.9 million. Cash and cash equivalents as of December 31, 2023, were $9.5 million, resulting in net debt of $85.5 million, an improvement of $0.9 million from the prior quarter. Net leverage was 2.9x at the end of fourth quarter 2023, down from 3.9x at the end of fourth quarter 2022. As of December 31, 2023, Manitex had total cash and availability of approximately $31 million.