I just crossed in Tumbes a few days ago. Unlike most countries, you need to clear Aduana before clearing Immigracion. First, a few kilometres before you reach the boarder, you need to stamp out of Ecuador. Then you enter the city through a sprawling market. There is a bridge. On the left is Ecuador Aduana, where you need to give your Ecuadorian permit. I didn't have one so i just passed by. Now, on the bridge are two flags, one for Ecuador, one for Peru. This is no-mans land! Here on the right you will find Aduana Peru. DO NOT PASS THIS OFFICE and proceed to Immigration, like i did. I was sent back to Aduana to get my permit first and the guy didn't want to issue it because i already entered without permision. It was a lot of work getting him to issue my permit, but in the end after a lot of stroking his ego, i got it. You will be sent to get coppies of your passport exit stamp and your licence, then the paperwork is very fast and simple. There is NO FEE for entering Peru.
Once in Peru, get ready to deal with the police. Between Trujillo and Lima, i have been stopped twice, and the third time i drove by the cop who was whistling at me and waving his arms. I carry a fake drivers licence which is a copy. It is obvious to them that it is a copy and they all say so, but they also know they have nothing to hold against me. The first guy said i was speeding (which i was) and asked me how fast i was going. I told him i was doing the speed limit ans asked him to see his radar, which he didn't have. He really wasn't pleased to see my fake licence, which i told him was a real Canadian licence and all i had. Realising i wasn't going to pay, he played really nice but pittiful cop and returned my licence. While getting back on the bike, he was almost begging me for a "refresco", i didn't oblige.
The next guy pulled me over outside of Lima on the truck rout. Apparently i wasn't allowed on this highway, which is probably true. The infraction was crossing a double solid line, which i did. He then informed me theat i was susposed to take the other highway, which we looked for on the GPS. I tell you, that interesting little device gets me out of so much trouble! He too was pissed that my licence was a fake, but he new that there was nothing he could do with me, so he let me go. The third guy was among a group of police that was busy extorting money from the locals at a tool booth outside of Lima. As i drove by, he started to whistle and wave his arms at me. I turned my head and ignored him and kept going. He obviously lost interest!
Remember, smile! Don't get angry, be very respectful, say your sorry and ask to leave, but NEVER pay them unless they write you an official ticket or you feel your life is in danger.