Ford van losing power uphill

I have a 1988 ford econoline van with about 160k miles on it. It was running ok, but of course not as good as it was when it was new, I towed a car home with it on a dolly and it did good with no problems, then the next day my husband used it to take the dolly back, the dolly came loose and went up under the van putting a hole in the back gas tank (which we patched) it was no big deal as that pump in that tank hasnt worked for a long time. He brought the van back and now it has no power I can be going 70 downhill and then by the time I get up the next medium sized hill it is at 45 mph and that is with the gas pedal floored. I dont think the dolly thing caused the problem but, thought I'd mention it. We did a complete oil change and new spark plugs, am not sure where to go from here. Any help would be appreciated!