His supporting cast hasn't looked nearly as good as he has this summer.
His offensive line has been a turnstile. His two young running backs can't hold onto the ball. His two trusted tight ends have combined for three catches and three injuries and the chemistry with his new slot receiver has been stalled by Wes Welker's sprained ankle.
A rash of injuries on defense. Special teams breakdowns. All-Pro linebacker Von Miller's six-game suspension that starts next week, which came on the heels of two executives getting suspended for drunken driving arrests.
It's enough to drive Broncos fans to regret putting money down on the Super Bowl favorites in Las Vegas.
Manning isn't sounding any alarms, however.
"I'd be a little concerned if we were a finished product and a finely oiled machine in the third preseason game," he said. "I want to be a well-oiled machine toward the end of the season and peak at that point."
The Broncos look a lot more like a creaky jalopy than a humming Ferrari right now.
Because they kick off the 2013 NFL season Sept. 5 against Super Bowl champion Baltimore, few starters figure to play much in the preseason finale Thursday night against Arizona, meaning Manning's preseason is over.
"I don't think you can get every question answered in the preseason," Manning said. "We have some young players, we have some first-year starters, potentially at tight end, and we're going to have a young running back.
In some ways, it's just like 2012, when Manning was getting used to just about everybody around him and needing the GPS to keep from getting lost on his way to and from work and home.
"I think, similar to last year, our goal is to improve throughout the season," Manning said. "By no means should we be a well-oiled machine going into our opener against Baltimore. Hopefully, we can be hitting on enough cylinders where we can be effective."
Denver lost three of its first five games last season before Manning settled in and turned the Broncos back into a powerhouse, albeit one that lost its first playoff game to the Ravens, something he said left a scar on the team's psyche.
The only salve for that wound is a Super Bowl title this season.
Welker, Tom Brady's favorite target in New England, bolted to the Broncos in free agency, teaming with young receivers Demaryius Thomas and Eric Decker, who combined for 23 TD catches last season, to form a new "Three Amigos" in Denver and prompting John Elway to declare he's jealous of Manning's targets.
Manning returned for his second season in Denver with a clean bill of health, more punch to his passes and noticeably more muscle tone to his right arm.
Plus, he just looks more comfortable in Denver than he did a year ago when he was starting his comeback from a series of neck injuries and surgeries that affected a nerve that runs into his right triceps and forced him to miss his final season in Indianapolis.
Even so, Manning said this has been another summer of change for him.
He's trying to develop a rapport with Welker, young running backs Ball and Ronnie Hillman and promising tight end Julius Thomas, a 6-foot-5, 250-pound target.
Then, there's new center Manny Ramirez, who hasn't snapped in a regular season game yet but has taken most of the snaps during the offseason with J.D. Walton, Dan Koppen and Ryan Lilja all getting hurt.
"There have been some changes for me," Manning said. "All those new players affect me."
Despite the patchwork O-line and running back foibles, Manning was able to complete 38 of 54 passes for 410 yards with three TDs and one interception in the exhibitions.
"It's really hard to know where you should be when you have new players," Manning said. "I just don't know enough about certain guys, I'm learning every day. Manny Ramirez and I are learning about each other. Julius Thomas and I are learning about each other. Montee Ball is learning the system, and I'm learning about him. I don't think you ever stop learning."
So, Manning will leave it to fans to wonder if the Broncos are ahead or behind as the new season approaches.
"I didn't have a set goal of where we should be right now. We are where we are and we have to make the best out of the players that are going to play for us and the injuries we have to overcome," Manning said. "We don't use any excuses. It is about doing the best with what we have."
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